arm: pmu: Fix non-devicetree probing

arm: pmu: Fix non-devicetree probing

There is a problem in the non-devicetree PMU probing where some
probe functions may get the number of supported events through
smp_call_function_any() using the arm_pmu supported_cpus mask.
But at the time the probe function is called, the supported_cpus
mask is empty so the call fails. This patch makes sure the mask
is set before calling the init function rather than after.

Signed-off-by: Mark Salter <[email protected]>
Signed-off-by: Jeremy Linton <[email protected]>
Signed-off-by: Will Deacon <[email protected]>