openfimg: compiler: Enclose SSA-specific data in a struct

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Implement trivial PHI insertion

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Include PHI statements in SSA dump

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>