powerpc/ftrace: Don't use lmw/stmw in ftrace_regs_caller()

For the same reason as commit a85c728c ("powerpc/32: Don't use
lmw/stmw for saving/restoring non volatile regs"), don't use
lmw/stmw in ftrace_regs_caller().

Use the same macros for PPC32 and PPC64.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ec286d2cc6989668a96f14543275437d2f3f0e3a.1645099283.git.christophe.leroy@csgroup.eu