PCI: microchip: Enable building driver as a module

Enable building driver as a module. The expected use case is the
driver is built as a module, is installed when needed, and cannot be
removed once installed since it is not possible to clean-up
the irq_chip data structures on removal, as described in:

https://lore.kernel.org/linux-pci/87y1wgbah8.wl-maz@kernel.org/

The driver has .suppress_bind_attrs set to true for the same
reasons (ie prevent unbinding, that would leave the kernel
with stale IRQ configuration that cannot be cleaned up).

Link: https://lore.kernel.org/linux-pci/87y1wgbah8.wl-maz@kernel.org/
Link: https://lore.kernel.org/r/20230728131401.1615724-3-daire.mcnamara@microchip.com


Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>