freedreno/ir3: do better job of marking convergence points

Fixes:
dEQP-GLES3.functional.shaders.switch.switch_in_do_while_loop_dynamic_vertex
dEQP-GLES3.functional.shaders.switch.switch_in_do_while_loop_dynamic_fragment

Signed-off-by: Rob Clark <robdclark@chromium.org>
10 jobs for !1194 with wip/deqp-fixes in 11 minutes and 58 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #412224
debian

00:03:12

 
  Build+Test
passed #412226
meson-clang

00:08:45

passed #412230
meson-clover

00:06:52

passed #412229
meson-main

00:06:03

passed #412225
meson-swr-glvnd

00:05:51

passed #412231
meson-vulkan

00:02:48

passed #412233
scons-llvm

00:03:46

passed #412232
scons-nollvm

00:05:42

passed #412227
scons-swr

00:08:37

passed #412228
scons-win64

00:06:22