pwm: qpnp: add PWM sync for 8994 PMIC

PWM channels in PMIC 8994 use sync to update
the PWM values.

Change-Id: I72e6bac2a94ec745957764c4a9904d7ba08786e9
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>