msm: qpnp-power-on: Add finer control of PMIC power off type

Modify the qpnp_pon_system_pwr_off() function so that different
types of PMIC reset may be requested.  In particular, add support
so that both warm and hard reset may be used.  Warm reset
maintains the hardware state of some PMIC peripherals.  Hard
reset resets all PMIC peripherals.

Change-Id: Ibe1491acfe90364e96b776d26e158522dfea9c2b
CRs-Fixed: 507850
Signed-off-by: David Collins <collinsd@codeaurora.org>