Managed resources in the driver should be automatically cleaned up on
driver detach. It's unnecessary to manually free/unmmap these resources.
One of the manual cleanup causes static checkers to complain.
The bug is reported by Dan Carpenter <dan.carpenter@oracle.com> in [1]

[1] https://www.spinics.net/lists/arm-kernel/msg593012.html

This patch gets rid of all the unnecessary manual cleanup and properly
unregister all the registered PMU devices by the driver on driver detach.
Signed-off-by: Tai Nguyen <ttnguyen@apm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>