arm: perf: dynamically allocate cpu hardware data

To support multiple PMUs, each PMU will need its own accounting data.
As we don't know how (in general) many PMUs we'll have to support at
compile-time, we must allocate the data at runtime dynamically

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>