freedreno/ir3: block reshuffling and loops!

freedreno/ir3: block reshuffling and loops!

This shuffles things around to allow the shader to have multiple basic
blocks.  We drop the entire CFG structure from nir and just preserve the
blocks.  At scheduling we know whether to schedule conditional branches
or unconditional jumps at the end of the block based on the # of block
successors.  (Dropping jumps to the following instruction, etc.)

One slight complication is that variables (load_var/store_var, ie.
arrays) are not in SSA form, so we have to figure out where to put the
phi's ourself.  For this, we use the predecessor set information from
nir_block.  (We could perhaps use NIR's dominance frontier information
to help with this?)

Signed-off-by: Rob Clark <robclark@freedesktop.org>