ARM: perf: handle armpmu_register failing

Currently perf_pmu_register may fail for several reasons (e.g. being
unable to allocate memory for the struct device it associates with each
PMU), and while any error is propagated by armpmu_register, it is
ignored by cpu_pmu_device_probe and not propagated to the caller.  This
also results in a leak of a struct arm_pmu.

This patch adds cleanup if armpmu_register fails, and updates the info
messages to better differentiate this type of failure from a failure to
probe the PMU type from the hardware or dt.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>