ARM: efistub: replace adrl pseudo-op with adr_l macro invocation

The ARM 'adrl' pseudo instruction is a bit problematic, as it does not
exist in Thumb mode, and it is not implemented by Clang either. Since
the Thumb variant has a slightly bigger range, it is sometimes necessary
to emit the 'adrl' variant in ARM mode where Thumb mode can use adr just
fine. However, that still leaves the Clang issue, which does not appear
to be supporting this any time soon.

So let's switch to the adr_l macro, which works for both ARM and Thumb,
and has unlimited range.

Reviewed-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>