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>