The Memory Controller provides a control register to check
if the video memory can be resized. The previous bootloader
might have locked this feature, which will be reflected by
this register.

This patch reads the control register before processing
a video memory resize request. An error code, -ENOTSUP,
is returned if the feature is locked.

Change-Id: Ia1d67f7a94aa15c6b18ff5c9b9b952e179596ae3
Signed-off-by: Anthony Zhou <anzhou@nvidia.com>