Fix context for embedded ARM workaround
Fix context for embedded ARM workaround

https://github.com/hugsy/gef/issues/320#issuecomment-553081021 suggests
a workaround for an inconsistenly named flag register on embedded ARM
systems. Unfortunately '$cpsr' was still hardcoded in this code which
caused context to fail even with the workaround.

hugsy/gef,hugsy/gef,hugsy/gef