freedreno/ir3: End VS with CHMASK and CHSH in GS pipelines

freedreno/ir3: End VS with CHMASK and CHSH in GS pipelines

When used in a GS pipeline, the VS doesn't end with the END
instruction. Instead it chains to the GS, which continues running with
the same register allocation.  The intended use cases seems to be that
you can compile a regular VS (ie outputs in registers and ending with
END) but then tack on link-time generated code past the END to write
the outputs using STLW, in case the VS is used with GS.

Signed-off-by: Kristian H. Kristensen <hoegsberg@google.com>