ARM: sleep.S: use PC-relative insn sequence for sleep_save_sp/mpidr_hash

Replace the open coded PC relative offset calculations with adr_l and
ldr_l invocations. This removes some open coded PC relative arithmetic,
avoids literal pools on v7+, and slightly reduces the footprint of the
code. Note that ALT_SMP() expects a single instruction so move the macro
invocation after it.

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