Make the r128 driver work without fbdev

[David Stanaway]

My system is running pretty well with Xinerama now, but there is a
problem with utilization of the video ram I think.

In OSX, I can have a 1600x1200 at 24bit and a 1152x768 at 24bit display, when
I try this configuration with Xorg + Alex's patches, it drops 1600x1200
and 1280x1024 modes on the second display due to insufficient memory.

It should need 8,414,208 + whatever bytes of ram, or if it uses a word
for each pixel, 11,218,944 + whatever bytes of ram.

I believe my r138 M3 has 16M of VRAM so there is some wasted allocation
somewhere.

I can run at these resolutions at 16bit, and here are the relevant
excerts from the log:
(--) R128(0): VideoRAM: 8192 kByte (128-bit SDR SGRAM 1:1)
(--) R128(1): VideoRAM: 4096 kByte (128-bit SDR SGRAM 1:1)

Now R128(0) has the 1152x768 display and at 16 bit, it should only need
1728 kByte for the framebuffer, and R128(1) which has 1600x1200 should
only need 3750 kByte for the frame buffer.

I will have a look through the driver to see if I can see where the
video memory is allocated, and see where the wasteage is, but that will
probably be tomorrow night before I get to look.

-- 
David Stanaway <david at stanaway.net>