Define implementor IDs, part numbers and Xscale architecture versions in
cputype.h.  Also create accessor functions for reading the implementor,
part number, and Xscale architecture versions from the CPUID regiser.
Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>