ARM: perf: replace arch_find_n_match_cpu_physical_id with of_cpu_device_node_get

arch_find_n_match_cpu_physical_id parses the device tree to get the
device node for a given logical cpu index. However, since ARM PMUs get
probed after the CPU device nodes are stashed while registering the
cpus, we can use of_cpu_device_node_get to avoid another DT parse.

This patch replaces arch_find_n_match_cpu_physical_id with
of_cpu_device_node_get to reuse the stashed value directly instead.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>