MIPS: sead3: Fix ability to perform a soft reset.

The soft reset register address and reset value to be written are
incorrect for the SEAD-3 platform. This patch fixes them such that
the SEAD-3 can actually perform a soft reset instead of causing an
exception. Also remove usage of 'include/asm/mips-boards/generic.h'
header file.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5454/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>