psxbios: merge from pcsxr

ckain's overflow fix (patch 13685)
psxmem: handle io mirrors

tested on real hardware (ignoring missing fault emulation)
fixes Star Wars - Episode I
cdrom: use single read/play cursor, handle cdlRead for cdda

cdlRead on cdda tested on real hardware
cdrom: stopping read should stop seek too
Fix PSX unmap issue causing crash on exit
psx_gpu: fix mask set in blend_blocks variant

thanks to Exophase for help with coming up with this fix
psx_gpu: minor test fixes
psx_gpu: fix line mask test
frontend: exit immediately on signals

.. and only hook them when compiled with frontend
frontend: sdl fixes
cdriso: handle no disk state better
frontend/menu: clean up cht loader
libretro: support disk control interface