drm: Add acquire ctx parameter to ->set_config

Surprisingly a lot of legacy drivers roll their own, for
runtime pm and because vmwgfx.

Also make nouveau's set_config static while at it.

Cc: Sinclair Yeh <syeh@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170322215058.8671-19-daniel.vetter@ffwll.ch