locore constructs an L2 page mapping the kernel and preloaded data
starting a KERNBASE (the same as VM_MIN_KERNEL_ADDRESS on arm64).
initarm() and pmap_bootstrap() use the preloaded metadata to
tell it where it can start allocating from.

pmap_bootstrap() currently iterates over the L2 page to find the last
valid entry, but doesn't do anything with the result. Remove the loop
and zap some now-unused local variables.