PCI: microchip: Align register, offset, and mask names with HW docs

Minor code re-organisation so that macros representing registers ascend in
numerical order and use the same names as their hardware documentation.
Removed registers not used by the driver.

Link: https://lore.kernel.org/r/20230728131401.1615724-4-daire.mcnamara@microchip.com


Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>