vga: adjust start-of-DMA fudge factors.
vga: adjust start-of-DMA fudge factors.

I should really move the latency-sensitive code path into assembler
so that its cycle count will stop changing.

cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib