x86: efi-x86_payload: Enumerate PCI bus during early boot

The generic efi payload currently does not enumerate the PCI bus,
which means peripherals on the PCI bus are not discovered by their
drivers. This uses board_early_init_r() to do the PCI enumeration.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>