Compatibility: VGA
Expects: AX    101bH
BX    first color register to convert
CX    number of color registers to convert
Returns: (none)
Info: This converts (sums) a range of DAC color values into gray-scale

The R,G,B of each of the specified registers is weighed according
to a BIOS internal system and replaced with values that are
displayed as shades of gray.

Notes:   In performing the conversion, the BIOS uses:
30% of the Red value
59% of the Green value
11% of the Blue value

  The BIOS performs gray-scale summing by default when it detects
a monochrome display.  That data may be found in the rMiscFlags
field of the VgaDynamicStateRec.

- -

INT 10H 101bH: Convert DAC Colors to Gray-Scale Values