panfrost: fix refcnt imbalance related to blitter
This issue is mainly a consequence of a call to util_blitter_clear() with unnecessary blitter states, these states are never freed.
This change is inspired from radeonsi and r600.
Note: PAN_SAVE_FRAGMENT_STATE is added and always enabled at this stage.
For instance, this issue is triggered on Mali-T720 with "piglit/bin/fcc-read-after-clear sample tex -auto -fbo", "piglit/bin/cubemap -auto" and "piglit/bin/fbo-srgb -auto" or on Mali-T820 with "piglit/bin/longprim -auto -fbo" and "piglit/bin/ext_render_snorm-render -auto -fbo" while setting GALLIUM_REFCNT_LOG=refcnt.log.
cc: mesa-stable
Signed-off-by: Patrick Lerda patrick9876@free.fr