arm64: add SIGSYS siginfo for compat task

SIGSYS is primarily used in secure computing to notify tracer of syscall
events. This patch allows signal handler on compat task to get correct
information with SA_SIGINFO specified when this signal is delivered.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>