Compile pci_host only once

Compile pci_host only once

Convert pci_host_conf_register_mmio_noswap(x) to
pci_host_conf_register_mmio(x, 0).

Convert pci_host_conf_register_mmio(x) to
pci_host_conf_register_mmio(x, 1) for big endian hosts, all cases
happen to be BE.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>