lima/ppir: add support for unconditional branches and condition negation

lima/ppir: add support for unconditional branches and condition negation

We need 'negate' modifier for branch condition to minimize branching. Idea
is to generate following:

current_block: { ...; if (!statement) branch else_block; }
then_block: { ...; branch after_block; }
else_block: { ... }
after_block: { ... }

Tested-by: Andreas Baierl <ichgeh@imkreisrum.de>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Reviewed-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>