openfimg: compiler: Remove OF_IR_NUM_CF_TYPES

There is no use for it and it only complicates switch statements.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Refactor make_ssa()

To improve readability, list handling is factored out of this function
and handling of other node types is split into pre- and post-order
parts, with subtree traversal code made common.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Destroy renames stack after SSA creation

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
openfimg: compiler: Implement dead code elimination

It seems to work fine, but IR needs to be modified to work on
per-component level, because SSA in current form treats assignments to
different components as new definitions...

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