Add support for virtIO Socket

[dreamliner787-9]

This PR:

• Add support for virtIO MMIO Socket device to allow point-to-point communication between VM guests without any Ethernet or IP protocols set up.
• Fix missing C bindings for VMM object.

Notes:

• The VMM config data structure has been changed to break out virtIO MMIO devices into individual types. Each type have a common regs struct that contains the MMIO region and vIRQ, in addition to any additional configuration data that may be required for that type. Currently, only the socket virtIO device requires additional config data. The updated config.h header is in Add virtio-socket device implementation libvmm#161