Add vita port made by rtype and various improvements

[Chips-fr]

• Vita port
• Typical config and fastmem in options.
• new virtual keyboard design
• disk switching using L & R for multidisk roms.

[r-type]

@Chips-fr Nice! btw if you have time can you check/try https://github.com/r-type/uae4arm-rpi-libretro it seem that it start to be playable (basic input) even if it is very WIP.

For vita part , if someone here with good vita knowledge can take a look at https://github.com/libretro/uae4arm-libretro/pull/9/files#diff-d675074306b4e82891c7254a3116483a before thinking to add an vita recipe. i've done things here but without good knowledge . so uae4arm work on my ps vita but not sure it's the right way of doing dynarec...

[inactive123]

@frangarcj Try to see if you're interested in the above.

[frangarcj]

I'll fix the Vita part later today