drm/i915: Mark getparam ioctl as DRM_UNLOCKED

With kms all the data getparam looks at is actually invariant, and
certainly not protected by the global kms mutex. With ums all the
setup code is already racy as hell, so this won't make things any
worse.

I've done this change so that all ioctl still used by kms drivers
are marked as DRM_UNLOCKED, besides that we obviously don't need
it any more in kms mode.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>