powerpc/book3s: Inline first level of update_mmu_cache()

update_mmu_cache() voids when hash page tables are not used.
On PPC32 that means when MMU_FTR_HPTE_TABLE is not defined.
On PPC64 that means when RADIX is enabled.

Rename core part of update_mmu_cache() as __update_mmu_cache()
and include the initial verification in an inlined caller.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bea5ad0de7f83eff256116816d46c84fa0a444de.1662370698.git.christophe.leroy@csgroup.eu