lib: arm: Implement flush_tlb_all

flush_tlb_all performs a TLBIALL, which invalidates the entire TLB and
affects only the executing PE; translation table walks are now Inner
Shareable, so execute a TLBIALLIS (invalidate TLB Inner Shareable) instead.
TLBIALLIS is the equivalent of TLBIALL [1] when the multiprocessing
extensions are implemented, which are mandated by the virtualization
extensions.

Also add the necessary barriers to tlb_flush_all and a comment to
flush_dcache_addr stating what instruction is uses (unsurprisingly, it's
DCCIMVAC, which does a dcache clean and invalidate by VA to PoC).

[1] ARM DDI 0406C.d, section B3.10.6

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>