ARM: nommu: add stub local_flush_bp_all() for !CONFIG_MMUU

Since the merging of Will's tlb-ops branch, specifically 89c7e4b8bbb3
(ARM: 7661/1: mm: perform explicit branch predictor maintenance when required),
building SMP without CONFIG_MMU has been broken.

The local_flush_bp_all function is only called for operations related to
changing the kernel's view of memory and ASID rollover - both of which are
irrelevant to an !MMU kernel.

This patch adds a stub local_flush_bp_all() function to the other tlb
maintenance stubs and restores the ability to build an SMP !MMU kernel.

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>