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>

include/uapi/linux/pci_regs.h

@@ -504,6 +504,12 @@
 #define  PCI_EXP_DEVCTL_URRE	0x0008	/* Unsupported Request Reporting En. */
 #define  PCI_EXP_DEVCTL_RELAX_EN 0x0010 /* Enable relaxed ordering */
 #define  PCI_EXP_DEVCTL_PAYLOAD	0x00e0	/* Max_Payload_Size */
+#define  PCI_EXP_DEVCTL_PAYLOAD_128B 0x0000 /* 128 Bytes */
+#define  PCI_EXP_DEVCTL_PAYLOAD_256B 0x0020 /* 256 Bytes */
+#define  PCI_EXP_DEVCTL_PAYLOAD_512B 0x0040 /* 512 Bytes */
+#define  PCI_EXP_DEVCTL_PAYLOAD_1024B 0x0060 /* 1024 Bytes */
+#define  PCI_EXP_DEVCTL_PAYLOAD_2048B 0x0080 /* 2048 Bytes */
+#define  PCI_EXP_DEVCTL_PAYLOAD_4096B 0x00a0 /* 4096 Bytes */
 #define  PCI_EXP_DEVCTL_EXT_TAG	0x0100	/* Extended Tag Field Enable */
 #define  PCI_EXP_DEVCTL_PHANTOM	0x0200	/* Phantom Functions Enable */
 #define  PCI_EXP_DEVCTL_AUX_PME	0x0400	/* Auxiliary Power PM Enable */