arm/arm64: Mark the phys_end parameter as unused in setup_mmu()

phys_end was used to cap the linearly mapped memory to 3G to allow 1G of
room for the vmalloc area to grown down. This was made useless in commit
c1cd1a2b ("arm/arm64: mmu: Remove memory layout assumptions"), when
setup_mmu() was changed to map all the detected memory regions without
changing their limits.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>