rockchip: video: vop: Reserve enough space for mipi dispaly

plat->size here is used to reserve frame buffer space befor relocation.
our mipi panel use 24 bitwidth, and vop require 32bit align. So the frame
buffer size should be at least 1920*1200*32/8.

Signed-off-by: Eric Gao <eric.gao@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>