[CSInfo][NFC] Interpret loaded parameter value separately

The collectCallSiteParameters() method searches for instructions
which load values into registers used for parameters passing.
Previously, interpretation of those values, loaded by one such
instruction, was implemented inside collectCallSiteParameters() method.

This patch moves the interpretation code from collectCallSiteParameters()
method into a separate static method named interpretValue. New method is
called from collectCallSiteParameters() to process each instruction from
targeted instruction scope.

The collectCallSiteParameters() searches for loaded parameter value
among instructions which precede the call instruction, inside the same
basic block. When needed, new method (interpretValue) could be used for
searching any instruction scope.

This is preparation for search of parameter value, loaded inside call
delay slot.

Patch by Nikola Tesic

Differential revision: https://reviews.llvm.org/D78106