ARM: OMAP2+: PMU: Convert OMAP2/3 devices to use HWMOD

Convert OMAP2/3 devices to use HWMOD for creating a PMU device. To support PMU
on OMAP2 devices we only need to use MPU sub-system and so we can simply use
the MPU HWMOD to create the PMU device. To support PMU on OMAP3 devices, we need
to use the MPU and DEBUG sub-systems and so use these HWMODs to create the PMU
device for OMAP3.

The MPU HWMOD for OMAP2/3 devices is currently missing the PMU interrupt and so
add the PMU interrupt to the MPU HWMOD for these devices.

This change also moves the PMU code out of the mach-omap2/devices.c files into
its own pmu.c file as suggested by Kevin Hilman to de-clutter devices.c.

Cc: Ming Lei <ming.lei@canonical.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@ti.com>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
[paul@pwsan.com: fixed checkpatch messages; updated to apply; dropped old-style
 initial filename line in header comments]
Signed-off-by: Paul Walmsley <paul@pwsan.com>