ARM: shmobile: rcar-gen2: Add watchdog support

This patch adds watchdog support by installing shmobile_boot_vector_gen2
to ICRAM1 when enough memory is available, in which case we also keep a
copy of MPIDR to complete the reset vector logic.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Signed-off-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>