xen/arm: Use register_t type of cpuinfo entries

xen/arm: Use register_t type of cpuinfo entries

All cpu identification registers that we store in the cpuinfo structure
are 64bit on arm64 and 32bit on arm32 so storing the values in 32bit on
arm64 is removing the higher bits which might contain information in the
future.

This patch is changing the types in cpuinfo to register_t (which is
32bit on arm32 and 64bit on arm64) and adding the necessary paddings
inside the unions.
For consistency uint64_t entries are also changed to register_t on 64bit
systems.

It is also fixing all prints using directly the bits values from cpuinfo
to use PRIregister and adapt the printed value to print all bits
available on the architecture.

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>