target/mips: Move msa_reset() to msa_helper.c

translate_init.c.inc mostly contains CPU definitions.
msa_reset() doesn't belong here, move it with the MSA
helpers.

One comment style is updated to avoid checkpatch.pl warning.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201215225757.764263-15-f4bug@amsat.org>
Tested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>