MIPS: Provide correct siginfo_t.si_stime

MIPS: Provide correct siginfo_t.si_stime

Provide correct siginfo_t.si_stime on MIPS64

Bug description:
MIPS version of copy_siginfo() is not aware of alignment on platforms with
64-bit long integers, which leads to an incorrect si_stime passed to signal
handlers, because the last element (si_stime) of _sifields._sigchld is not
copied. If _MIPS_SZLONG is 64, then the _sifields starts at the offset of
4 * sizeof(int).

Patch description:
Use the generic copy_siginfo, which doesn't have this problem.

Signed-off-by: Petr Malat <oss@malat.biz>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8671/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>