Feature: Set value of global register

[CouleeApps]

What is the feature you'd like to have?
On some architectures (eg PPC), certain registers are considered "Global" (eg r2) and are not considered by dataflow. There should be a way to set these registers to a constant value at the start of a function, considering they do not have variables created which you can use Set User Variable Value on.

Is your feature request related to a problem?
I wanted to reverse a PPC binary and my HLIL is full of -1234(r2) with no way to tell binja what r2 should be.

Are any alternative solutions acceptable?
Could do a more general approach of "set any register to a PossibleValueSet at start of function"

Additional Information:
Binary available upon request

[fuzyll]

This was completed at some point between 4.1 and 4.2, although we currently only allow a single global register. Support for multiple is tracked now by #6096.