arm64: drop redundant macros from read_cpuid()

asm/cputype.h contains a bunch of #defines for CPU id registers
that essentially map to themselves. Remove the #defines and pass
the tokens directly to the inline asm() that reads the registers.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>