powerpc/kuap: Prepare for supporting KUAP on BOOK3E/64

Also call kuap_lock() and kuap_save_and_lock() from
interrupt functions with CONFIG_PPC64.

For book3s/64 we keep them empty as it is done in assembly.

Also do the locked assert when switching task unless it is
book3s/64.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1cbf94e26e6d6e2e028fd687588a7e6622d454a6.1634627931.git.christophe.leroy@csgroup.eu