x86/percpu: Unify percpu read-write accessors

Redefine percpu_from_op() and percpu_to_op() as __raw_cpu_read()
and __raw_cpu_write().  Unify __raw_cpu_{read,write}() macros
between configs w/ and w/o USE_X86_SEG_SUPPORT in order to
unify {raw,this}_cpu{read_write}_N() accessors between configs.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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/20240430091833.196482-3-ubizjak@gmail.com