freedreno/a3xx/compiler: make compiler errors more useful

freedreno/a3xx/compiler: make compiler errors more useful

We probably should get rid of assert() entirely, but at this stage it is
more useful for things to crash where we can catch it in a debugger.
With compile_error() we have a single place to set an error flag (to
bail out and return an error on the next instruction) so that will be a
small change later when enough of the compiler bugs are sorted.

But re-arrange/cleanup the error/assert stuff so we at least get a dump
of the TGSI that triggered it.  So we see some useful output in piglit
logs.

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