Implement set_type() to allow configuration of the trigger type.

Cc: Abhijeet Dharmapurikar <adharmap@quicinc.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>