[PSX] Support for non-retail BIOS

[frarees]

It seems mednafen is already able to handle this (related discussion https://forum.fobby.net/index.php?t=tree&th=1939)

UX Proposal 1:

• Let users load the additional files (i.e. PSX-XBOO.ROM and PSXONPSP660.BIN), the same way it does with retail BIOS, and have it check against specific MD5s.
• Let users decide (via e.g. radio buttons) to use retail (will pick based on region) or any of the other ones (picked specificially i.e. I want to load with the PSP dumped BIOS).

UX Proposal 2:

• Let users load one additional custom BIOS file, no checksum validation.
• Let users specify if they want to use the custom BIOS over the retail ones (or simply, if there's a custom BIOS specified, just go for it).

IMO the second proposal would be the least convoluted, and can be easily delivered as an advanced-only feature (Secrets?).

[clobber]

I would confirm with Ryphecha first if there are any compatibility issues before I added support for this. Downloading the original retail BIOS files are not a big deal, so I don't care too much about this BIOS that was ripped from PSP firmware.

[frarees]

I would confirm with Ryphecha first if there are any compatibility issues before I added support for this.

👍

Downloading the original retail BIOS files are not a big deal, so I don't care too much about this BIOS that was ripped from PSP firmware.

Yeah not an issue at all. I was more interested in the differences from those BIOS vs the retail ones (e.g. no boot screen).