Fixes bug where after changing settings in the big picture UI, if you
didn't have a game running, it would turn off vsync, making GPU go brr.
Also cleans up HostDisplay a bit, removing redundant parameters.
Guest memory is now mapped into a shared memory/file mapping, for use
with fastmem.
64-bit and 128-bit arguments are passed by register/value instead of by
reference/address.
LDL/LDR/SDL/SDR now use 64-bit GPRs instead of SSE.