PCI: Add PCIE_PME_TO_L2_TIMEOUT_US L2 ready timeout value

Add the PCIE_PME_TO_L2_TIMEOUT_US macro to define the L2 ready timeout
as described in the PCI specifications.

Link: https://lore.kernel.org/r/20230821184815.2167131-2-Frank.Li@nxp.com
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>

Author: nxpfrankli

drivers/pci/pci.h

@@ -13,6 +13,12 @@
 
 #define PCIE_LINK_RETRAIN_TIMEOUT_MS	1000
 
+/*
+ * PCIe r6.0, sec 5.3.3.2.1 <PME Synchronization>
+ * Recommends 1ms to 10ms timeout to check L2 ready.
+ */
+#define PCIE_PME_TO_L2_TIMEOUT_US	10000
+
 extern const unsigned char pcie_link_speed[];
 extern bool pci_early_dump;