vibrator: cs40l25: add pwle_ramp_down feature

Add the pwle_ramp_down feature and set the ramp down time to be 50 ms to
match with frameworks

Bug: 200713702
Test: verified that pwle_ramp_down node works as expected, there is no
click effect when a waveform is cancelled and regression testing passed

Change-Id: Id75cf8c4456b22887135bd7bf206516f26415157
Signed-off-by: Vince Leung <leungv@google.com>
6 files changed