arm64: Move some macros under #ifndef __ASSEMBLY__

Several macros for various x_to_y exist outside the bounds of an
__ASSEMBLY__ guard. Move them in preparation for support for
CONFIG_DEBUG_VIRTUAL.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>