Note that this doesn't differentiate (due to lack of information in
video_priv) between different possible component orders for 32bpp.
But the main user at this point is efi_loader, and GOP expects xBGR
so any video drivers that this is incorrect for already have problems.
(Also, conveniently, this matches what simple-framebuffer bindings
expect for kernels that use the simple-framebuffer DT binding to
take over the bootloader display.)