efi: Add video support to the app

The current EFI video driver only works when running in the stub. In that
case the stub calls boot services (before jumping to U-Boot proper) and
copies the graphics info over to the efi table. This is necessary because
the stub exits boot services before jumping to U-Boot.

The app maintains access to boot services throughout its life, so does not
need to do this. Update the driver to support calling boot services
directly.

Enable video output for the app. Note that this uses the
EFI_GRAPHICS_OUTPUT_PROTOCOL protocol, even though it mentions vesa.

A sample qemu command-line for this case is:

   qemu-system-x86_64 -bios /usr/share/edk2.git/ovmf-ia32/OVMF-pure-efi.fd
   -drive id=disk,file=try.img,if=none,format=raw -nic none
   -device ahci,id=ahci -device ide-hd,drive=disk,bus=ahci.0

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>