build.mk: build arm-clock stub

forgot to build the arm-clock stub, which will cause
a NULL pointer dereference when we turn the mmu on.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
mmu: remove overloaded align_up and align_down

align.hh functions with the name name can be used instead
without any downside, and with the upside of less confusion.

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

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>
aarch64: add page tables, MMU

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