powerpc: Activate HAVE_RELIABLE_STACKTRACE for all

CONFIG_HAVE_RELIABLE_STACKTRACE is applicable to all, no
reason to limit it to book3s/64le

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/955248c6423cb068c5965923121ba31d4dd2fdde.1615881400.git.christophe.leroy@csgroup.eu