PCI: layerscape(ep): Rename pf_* as pf_lut_*

'pf' and 'lut' are two different acronyms describing the same
thing, basically it is a MMIO base address plus an offset.

Rename them to avoid duplicate pf_* and lut_* naming schemes in the
driver.

Link: https://lore.kernel.org/r/20231204160829.2498703-4-Frank.Li@nxp.com
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Roy Zang <Roy.Zang@nxp.com>