MIPS: SEAD3: Use generic restart-poweroff driver

MIPS: SEAD3: Use generic restart-poweroff driver

Remove the custom platform code to restart when instructed to power off,
instead relying upon the generic restart-poweroff driver probed via DT
to do the same thing.

Remove also the halt implementation, which is incorrect. The generic
MIPS version will hang the system as halt should.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jacek Anaszewski <j.anaszewski@samsung.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14057/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>