Implement 8bpp chunky raster ops

[kelihlodversson]

The only major VDI feature missing still is rendering of raster blocks.
In bitplane modes this is handled by complicated and optimized 68k assembly.

vro_cpyfm and vrt_cpyfm:

For our purposes the 8bpp packed pixel implementation can be implemented in straightforward C.
We need to support the following situations:

• blit 1bpp source to 8bpp packed pixel with fg color.
• blit 8bpp to 8bpp

And we may need one or both of these (FVDI seems to not support these.)

• 4bpp (packed pixel - two pixels in a byte) to 8bpp.
• 2bpp (packed pixel - 4 pixels per byte) to 8bpp.

vr_trnfm:

For converting MFDBs from standard to device specific format (and vice versa), we need to support:

• 8 planes to/from 8bpp packed pixel
• 1bpp is the same in both packed and standard format, so it's a no-op/pure memcpy

In case we implement the 4 and 2bpp blits above, vr_trnfm needs to additionally support these:

• 4 planes to/from 4bpp packed pixel
• 2 planes to/from 2bpp packed pixel

[paulwratt]

Some of these may already be available in FVDI (no sure yet).

There are bitplane handling functions in XaAES (texture loaders) and Highwire (image handlers) sources. I also have a bunch of chunky functions that handle 256 colors to 32bit in various formats. ALL of these mentioned are coded in C not assembler.

Note that I also have some C code to handle VDI colors/palettes. Also, although handling 32bit color modes is faster (RPi native), you can set (force) as low as 2bit color mode. 2bit color in memory would look like a ST, but maybe RPi has enuf speed to convert that to or use 32bit mode with mono colors of ur choosing?

colorspc.c.txt