PCI: mvebu: Add support for compiling driver as module

PCI: mvebu: Add support for compiling driver as module

Now when driver uses devm_pci_remap_iospace() function, it is possible
implement ->remove() callback for unbinding device from driver.

Implement mvebu_pcie_remove() callback with proper cleanup phase, drop
driver's suppress_bind_attrs flag and switch type of CONFIG_PCI_MVEBU
option from bool to tristate.

This allows to compile pci-mvebu.c driver as loadable module pci-mvebu.ko
with ability to unload it.

Link: https://lore.kernel.org/r/20211126144307.7568-3-pali@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>