asahi: Track write to separate stencil
From the commit message of 94f7c011 ("v3d: Track write reference to the separate stencil buffer."), anholt says:
Otherwise, a blit from separate stencil may fail to flush the job that initialized it, or new drawing could fail to flush a blit reading from stencil.
Fixes dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_stencil_only
Signed-off-by: Alyssa Rosenzweig alyssa@rosenzweig.io