PCI: cadence: Allow pci_host_bridge to have custom pci_ops

Certain platforms like TI's J721E allows only 32-bit configuration
space access. In such cases pci_generic_config_read and
pci_generic_config_write cannot be used. Add support in Cadence core
to let pci_host_bridge have custom pci_ops.

Link: https://lore.kernel.org/r/20200722110317.4744-7-kishon@ti.com


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>