xen/arm: Limit the scope of cpregs.h

xen/arm: Limit the scope of cpregs.h

Currently, cpregs.h is indirectly included every files of the hypervisor even
for arm64. However, the only use for arm64 is when emulating co-processors.

For arm32, all users of processor.h expect cpregs.h to be included in
order to access co-processors. So move the inclusion in
asm-arm/arm32/processor.h.

cpregs.h will also be directly included in the co-processors emulation
to accommodate arm64.

This is drastically reducing the exposure of cpregs.h to any source file
on arm64.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>