ARM: kernel: enhance MPIDR macro definitions

Kernel subsystems other than the topology layer need the MPIDR
mask definitions to access the MPIDR without relying on hardcoded
masks. This patch moves the MPIDR register masks definition to
a header file and defines a macro to simplify access to MPIDR bit fields
representing affinity levels.

Change-Id: I06312e79c1564744b1bfb21b8c54b432866c7ad1
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>