MIPS: Malta: Remove custom halt implementation

The arch code will hang the machine with an infinite loop if the board
doesn't provide an impelementation of halt - let it, rather than
duplicating it.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14280/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>