[WiP] drm/exynos: Further WiP on S3C6410 G3D driver

Changes done:
 - fixed context destruction handling to abort pending submits,
 - reworked state restore to decouple state apply/restore from state
   update,
 - handle internal state update before powering on/flushing the GPU,
 - flush pipeline on state update depending on which parts are dirty,
 - add missing shader data state restoration.