Signed-off-by: Paul A. Clarke <[email protected]>

Produces JSON representation of instructions, operands, opcode layouts, etc.
Not claimed to be exhaustive.

Depends on https://github.com/ThinkOpenly/riscvdecode.

Signed-off-by: Paul A. Clarke <[email protected]>

…istently

More support for ThinkOpenly#4.
Using the `extension()` function in `mapping clause encdec` expressions for extensions allows a parser to clearly know when a function is part of an extension (or set of extensions).

…e.sail

Added instruction names and descriptions

* Adds names for instructions in `riscv_insts_base.sail` using the attributes approach

* Descriptions are added to instructions in the same file using the doc comments approach

Currently, when executing `make json`, the command itself is echoed,
causing issues with the JSON representation.

This PR Suppress this echoing, ensuring a proper JSON output
without the need for any manual editing later on.

Some instructions are grouped in a single `mapping clause assembly`
where the respective mnemonics are embedded within a separate `mapping`.

For instructions which are _not_ grouped, the name of the instruction
can be added as an attribute to any of the instruction-specific constructs.

For grouped instructions, the attribute needs to be added to a construct
at the granularity of the specific instruction. Here, we attach the
attribute within the individual element of the `mapping` that includes
the actual instruction mnemonic.

This approach is still insufficient for mnemonics that are constructed:
```
mapping clause assembly = VLSEGTYPE(nf, vm, rs1, width, vd)
  <-> "vl" ^ nfields_string(nf) ^ "e" ^ vlewidth_bitsnumberstr(width) ^ ".v" [...]
```
...so more thought is needed here.

Also, I'm settling on a convention of using lower case (not Leading Caps),
at least for now. This matches how the instruction names are written in
the ISA specification, at least for those instructions for which the name
is actually provided. :-/

* Move definition of function of `extension`
* Utilize extension() instead of `haveZmmul()`
* Utilize extension() instead of `haveUsrMode()`
* Utilize extension() instead of `haveSupMode()`
* Utilize extension() instead of `haveNExt()`
* Utilize extension() instead of `haveZkr()`
* Utilize extension() instead of `haveUsrMode()`
* Move comments from `have*` functions into `extension` function
* Delete all unused  `have*` definitions of various extensions

Fixes ThinkOpenly#4 .

Authored-by: Joydeep Tripathy <[email protected]>

GitHub CI is complaining:
```
fix end of files.....................Failed
- hook id: end-of-file-fixer
- exit code: 1
- files were modified by this hook

Fixing doc/JSON.md
[...]
All changes made by hooks:
diff --git a/doc/JSON.md b/doc/JSON.md
index 82170ef..fc7f9cc 100644
[...]
-4.  Within that clone : `make json`
\ No newline at end of file
+4.  Within that clone : `make json`
Error: Process completed with exit code 1.
```

The JSON backend extracts function code verbatim into JSON format.
Unfortunately, the Unicode "Less-than Or Equal To" character, when embedded in
JSON, even when escaped using OCaml `String.escaped` does not successfully parse
with Python (3.10.12).

For now, at least, revert the Unicode symbol to the ASCII equivalent, which is
exactly what is used in the corresponding code and thus might even reduce the
chance of confusion.