lxfb: fix console blanking

Simply enabling DAC blanking without turning off the CRT seems to be resulting
in characters remaining on the screen when the monitor blanks.  This patch
turns off the CRT for all modes, and also powers down the DACs when vsync
and/or hsync are disabled.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Acked-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>