x86/percpu: Rename percpu_stable_op() to __raw_cpu_read_stable()

Rename percpu_stable_op() to __raw_cpu_read_stable() to be
in line with other read/write percpu accessors.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240520080951.121049-1-ubizjak@gmail.com