exceptions: add accessors for pc and error

in order to share most of the fault code in core/mmu.cc,
we add accessors to get the program counter and an error
code whose interpretation is arch-dependent
(error_code for x64, ESR for AArch64).

This also fixes an issue in jvm_balloon, where the
error code was checked incorrectly.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: create initial page tables

create the initial page tables for TTBR0 / TTBR1
and set up the registers for the MMU.

Signed-off-by: Jani Kokkonen <jani.kokkonen@huawei.com>
Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
arch: add flush_tlb

add the API arch::flush_tlb and the implementation
for x64 and aarch64.

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>