xen/arm64: sysreg: Implement the 32-bit helpers using the 64-bit helpers

xen/arm64: sysreg: Implement the 32-bit helpers using the 64-bit helpers

Clang is pickier than GCC for the register size in asm statement. It
expects the register size to match the value size.

The instructions msr/mrs are expecting a 64-bit register. This means the
implementation of the 32-bit helpers is not correct. The easiest
solution is to implement the 32-bit helpers using the 64-bit helpers.

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