freedreno/a4xx: fix fragcoord.z + fragdepth

freedreno/a4xx: fix fragcoord.z + fragdepth

It seems like disabling earlyz on a4xx also, by defaults, disables
fragcoord.z to the FS.  For frag shaders that both read fragcoord(.z)
and write fragdepth, we need to set some extra bits to prevent a
lockup.

This lets us get rid of the hack of disabling fragcoord.z (which
prevented 0ad from lockups, but resulted in rendering corruption).  Also
fixes fbo-depth-sample-compare.

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