HLE: sceUsb stubs.
Improve cross-platform savestate compat.

If 0 files are open in flash0:, which is very very common, this will make
them work the same.
Disable dithering (which affects pixel download.)

Fixes #6494.
Correct async packing alignment.

Only matters if a framebuffer width is not a multiple of 4, which might
not happen anyway.
Merge pull request #6500 from unknownbrackets/danganronpa-hack

Disable dithering
Use the CPU for download on non-NVIDIA cards.

Fixes #6494.
Delete temporary/blitting FBOs on device lost.

Fixes issues when the device goes to sleep with Danganronpa, block
transfers, etc.
When applying the Danganronpa hack, force 5551.

This prevents dithering from happening during the blit, and since
dithering is off during drawing, allows the colors to be correct on some
devices which always dither during blits.
Merge pull request #6502 from unknownbrackets/danganronpa-hack2

When applying the Danganronpa hack, force 5551
Merge pull request #6493 from xsacha/master

HLE: sceUsb stubs.
Fix savestates broken by #6493.