dm: common: Add memory reservation for the video uclass

dm: common: Add memory reservation for the video uclass

Before relocation we need to reserve memory for the video driver frame
buffers so that they can use this memory when they start up (after
relocation). Add a call to the uclass to permit this.

The current top and bottom of the region is stored in global_data so that
it can be checked post-relocation to ensure enough memory is available. No
video device should be probed before relocation.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>