Some bits in PCI_EXP registers are reserved for non-root ports. Driver
pci-bridge-emul.c implements PCIe Root Port device therefore it should not
allow setting reserved bits of registers.

Properly define non-reserved bits for all PCI_EXP registers.

Link: https://lore.kernel.org/r/20211124155944.1290-5-pali@kernel.org
Fixes: 23a5fba4 ("PCI: Introduce PCI bridge emulated config space common logic")
Signed-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org