powerpc/64s: make linear_map_hash_lock a raw spinlock

This lock is taken while the raw kfence_freelist_lock is held, so it
must also be a raw spinlock, as reported by lockdep when raw lock
nesting checking is enabled.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221013230710.1987253-3-npiggin@gmail.com