lrdpv2: Compute program counter based on other GPRs for msm8996

In certain reset scenarios, Program Counter value is not retained
across reset. Implement logic to approximate Program Counter based on
other General Purpose Registers. This should help get the CPU
context from crash dumps when original Program Counter value is
NULL or invalid.

Change-Id: Iacffc4103df1d482682bc7c1e6b83a55981ca78d