ARM: oprofile: Rename op_arm to oprofile_perf

In preparation for moving the generic functions out of this file, give
the functions more general names (e.g. remove "arm" from the names).

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>