msm: qpnp-haptic: add test interfaces for pwm mode

Add couple of test interfaces for pwm mode - ramp and min_max
sequences. PWM is played through a dtest line which is to be
configured from DT.

Change-Id: I69c32606c46b54c0fb23065ae5447da0fc311db9
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>