Perf: Add debugfs node to clear PMU

Create debugfs node to clear PMU and some internal variables
used by Perf code. This provides a recovery path for
PMU related unexpected error scenarios.

Change-Id: I88ae9dda0888db9316ce123f6f3a58faec4d69ee
Signed-off-by: Sheetal Sahasrabudhe <sheetals@codeaurora.org>

Conflicts:
	arch/arm/Kconfig