passthrough: Fix pci bar remapping when guest probes width with all-1 BAR

passthrough: Fix pci bar remapping when guest probes width with all-1 BAR

When guest code tries to get the block size of mmio, it will write all "1"s
into pci bar register and then qemu will return all "0"s to the don't care
bits in the emulated bar register to indicate the block size to guest code.
In this case, we should not create p2m mapping in  pt_bar_reg_write() and
pt_exp_rom_bar_reg_write(). Attached patch fixes this issue, additional
comment can be found in the patch.

Signed-off-by: Wei Wang <wei.wang2@amd.com>