fix radeondrm console colours on sparc64

fix radeondrm console colours on sparc64

Directly do register writes in the sparc64 specific
radeondrm_setcolor() instead of trying to pass colour values via
crtc->gamma_store.  With these changes the console changes from
white text on a black background to black text on a white background.

Only older radeon families are handled and crtc selection is
skipped as with radeonfb.  Both of the sun radeon parts fall
into this family < CHIP_RS600 path.

xvr-100 (0x1002:0x5159 pci rv100)
xvr-300 (0x1002:0x5b64 pcie rv380)

Tested on a Sun Blade 100 with XVR-100 by Ted Bullock
who also helped with the patch.