ARM: p2v: use relative references in patch site arrays

Free up a register in the p2v patching code by switching to relative
references, which don't require keeping the phys-to-virt displacement
live in a register.

Acked-by: Nicolas Pitre <nico@fluxnic.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>