anv: Only re-emit non-dynamic state that has changed.

On commit f6e7de41, we started emitting 3DSTATE_LINE_STIPPLE as part
of the non-dynamic state. That gets re-emitted every time we bind a new
VkPipeline. But that instruction is non-pipelined, and it caused a perf
regression of about 9-10% on Dota2.

This commit makes anv_dynamic_state_copy() return a mask with only the
state that has changed when copying it. 3DSTATE_LINE_STIPPLE won't be
emitted anymore unless it has changed, fixing the problem above.

v2: Improve commit message and add documentation about skipped checks
(Jason)

Fixes: f6e7de41 ("anv: Implement VK_EXT_line_rasterization")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 2b7ba9f2)