mmu: add flush_tlb_all and flush_tlb_local APIs

flush_tlb_all flushes the TLBs for all CPUs in the cluster,
while flush_tlb_local only affects the current CPU.

Move the implementations to the arch-specific mmu.cc,
and the definitions to mmu-defs.hh

Signed-off-by: Jani Kokkonen <jani.kokkonen@huawei.com>
Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: add page tables, MMU

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
mmu: implement mmu for aarch64 with refactoring of x64

Signed-off-by: Jani Kokkonen <jani.kokkonen@huawei.com>
Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: remove most AARCH64_PORT_STUB related to MMU

also enable core/pagecache.cc in the AArch64 build.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>