dt-bindings: soc: qcom: add PMIC PON log bindings

Add Qualcomm Technologies, Inc. PMIC PON log device bindings.  The
PMIC PON log device parses power-on, power-off, and fault messages
stored in a binary log within the SDAM memory found on some QTI
PMIC devices.

Change-Id: If537d6abeebbdb93d01b268442bff1ba72c101ab