panfrost/midgard: Verify SSA claims when pipelining

panfrost/midgard: Verify SSA claims when pipelining

The pipeline register creation algorithm is only valid for SSA indices;
NIR registers and such cannot be pipelined without more complex
analysis. However, there are the ocassional class of "liars" -- indices
that claim to be SSA but are not. This occurs in the blend shader
prologue, for example. Detect this and just bail quietly for now.

Eventually we need to rewrite the blend shader prologue to occur in NIR
anyway (which would mitigate the issue), but that's more involved and
depends on a better understanding of pixel formats in blend shaders (for
non-RGBA8888/UNORM cases).

Fixes some blend shader regressions.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>