irqchip: armada-370-xp: properly request resources

Instead of using of_iomap(), we now use of_address_to_resource(),
request_mem_region() and ioremap(). This allows the corresponding I/O
regions to be properly requested and visible in /proc/iomem.

The main motivation for this change is that the introduction of the
MSI support requires us to get the physical address of the main
interrupt controller registers, so we will need the corresponding
'struct resource' anyway.

We also take this opportunity to change a panic() to BUG_ON(), in
order to be consistent with the rest of the driver.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Daniel Price <daniel.price@gmail.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>