drivers/perf: kill armpmu_register

Nothing outside of drivers/perf/arm_pmu.c should call armpmu_register
any more, so it no longer needs to be in include/linux/perf/arm_pmu.h.
Additionally, by folding it in to arm_pmu_device_probe we can allow
drivers to override struct pmu fields without getting blatted by the
armpmu code.

This patch folds armpmu_register into arm_pmu_device_probe. The logging
to the console is moved to after the PMU is successfully registered with
the core perf code.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Suggested-by: Will Deacon <will.deacon@arm.com>
Cc: Drew Richardson <drew.richardson@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>