powerpc/85xx: Drop CONFIG_VIDEO on P1_P2_RDB-PC boards to reduce size

With older compilers (gcc-4.2.x) we run into issues that resulting image
is too large.  We can save a bunch of space by removing the video support.
In general video support on these boards is a nice to have since it
requires a PCIe add-on card.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>