ARM: mpu: Complete initialisation of the MPU after reaching the C-world

Much like with the MMU, MPU initialisation is performed in two stages; the
first in the pre-C world and the 'real' initialisation during arch setup.

This patch wires in previously added MPU initialisation functions so that
the whole of memory is mapped with the appropriate region properties for
'normal' RAM (the appropriate properties depend on whether the system is
SMP).

Stub initialisation functions are added for the case that there MPU support
is not configured in to the kernel.

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
CC: Hyok S. Choi <hyok.choi@samsung.com>