PCI: endpoint: Add pci_epf_align_inbound_addr() helper for inbound address alignment

Add pci_epf_align_inbound_addr() to align the inbound addresses according
to PCI BAR alignment requirements. The aligned base address and offset are
returned via 'base' and 'off' parameters.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
[mani: reworded kernel-doc and commit message]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20250710-ep-msi-v21-5-57683fc7fb25@nxp.com