ARM: Factor out cpuid implementor and part number

Decoding the implementor and part number of the CPU id in the CPU ID
register is needed by KVM, so we factor it out to share the code.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>
Conflicts:

	arch/arm/kernel/perf_event_cpu.c

Conflicts:
	arch/arm/kernel/perf_event_cpu.c