x86: bios: Allow pci config read/write to host bridge in int1a_handler

We should allow pci config read/write to host bridge (b.d.f = 0.0.0)
in the int1a_handler() which is a valid pci device.

Signed-off-by: Jian Luo <jian.luo4@boschrexroth.de>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>