ARM: mvebu: improve PMSU driver to request its resource

Until now, the PMSU driver was using of_iomap() to map its registers,
but of_iomap() doesn't call request_mem_region(). This commit fixes
the memory mapping code of the PMSU to do so, which will also be
useful for a later commit since we will need to adjust the resource
base address and size for Device Tree backward compatibility.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1397483433-25836-4-git-send-email-thomas.petazzoni@free-electrons.com
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>