Perf: arm64: Add debugfs node to clear PMU

Create debugfs node to clear PMU and some internal variables
used by Perf code. This provides the user with a recovery
path in case of PMU related unexpected error scenarios.

Change-Id: I4e62a51043d7dcaa21b551ce6a6715486ef46cca
Signed-off-by: Sheetal Sahasrabudhe <sheetals@codeaurora.org>