Specify trigger type=2 in trigger.S (#425)

* Specify trigger type=2 in trigger.S

Previous tests implicitly assume triggers only support type=2. However,
a trigger may support multiple types, i.e., type=15. This commit
explicitly specifies type=2 in trigger.S to support type 15.

* Update debug/programs/trigger.S

Co-authored-by: Tim Newsome <tim@sifive.com>
Signed-off-by: YenHaoChen <39526191+YenHaoChen@users.noreply.github.com>

Signed-off-by: YenHaoChen <39526191+YenHaoChen@users.noreply.github.com>
Co-authored-by: Tim Newsome <tim@sifive.com>