mach-mx5/devices.c: Add PMU device

Author: unknown so far, from community. This patch is needed
for oprofile to work.

Signed-off-by: Leonardo Sandoval <b42214@freescale.com>
Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
Signed-off-by: Mahesh Mahadevan <Mahesh.Mahadevan@freescale.com>