PCI: cadence: Convert all r/w accessors to perform only 32-bit accesses

PCI: cadence: Convert all r/w accessors to perform only 32-bit accesses

Certain platforms like TI's J721E using Cadence PCIe IP can perform only
32-bit accesses for reading or writing to Cadence registers. Convert all
read and write accesses to 32-bit in Cadence PCIe driver in preparation
for adding PCIe support in TI's J721E SoC.

Also add spin lock to disable interrupts while modifying PCI_STATUS
register while raising legacy interrupt since PCI_STATUS is accessible
by both remote RC and EP and time between read and write should be
minimized.

Link: https://lore.kernel.org/r/20200722110317.4744-5-kishon@ti.com
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>