staging: sm7xxfb: dead code removal

This patch removes dead code related to BaseAddressInVRAM. It fixes
comment on RAM control bits too.

Tested with SM712.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>