PCI: Add PCI_EXP_DEVCTL_PAYLOAD_* macros

Define a macro PCI_EXP_DEVCTL_PAYLOAD_* for every possible Max Payload
Size in linux/pci_regs.h, in the same style as PCI_EXP_DEVCTL_READRQ_*.

Link: https://lore.kernel.org/r/20211005180952.6812-2-kabel@kernel.org


Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>