video: mb862xxfb: use pre-initialized configuration for PCI GDCs

If the bootloader has already initialized the display
controller, do not re-initialize it in the driver. Take over
the bootloader's configuration instead. This is already supported
for non PCI GDCs Lime and Mint. Add this functionality for PCI
GDCs Coral-P and Coral-PA. It is useful to avoid flicker and
also avoids unneeded init delays while booting.

Signed-off-by: Anatolij Gustschin <agust@denx.de>