openfimg: compiler: Fix propagation of split dst variables to PHIs

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Avoid removing MOVs with modifiers in copy elimination

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Add MOV removal pass

It handles only simple var-to-var moves without modifiers, which in SSA
form are essentially no-ops, because every assignment always creates new
variable.

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