gpu: nvgpu: bring back tegra idle registration

To make do_idle work when nvgpu is built as a module, reverse the order
of call dependencies for do_idle. Don't provide visible
gk20a_do_{idle,unidle}() functions for the kernel but instead call the
kernel for registering and unregistering pointers to them when the
driver loads and unloads.

Refactor the internal __gk20a_do_{idle,unidle} functions to take a
struct gk20a * instead of struct device *, and use the callback api for
providing that g instead of retrieving the plat device from device tree.

Bug 200290850

Change-Id: Ibef8b069302e547b298069cbb97734f461a10cc3
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-on: http://git-master/r/1493774
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c

@@ -13,8 +13,6 @@
  * more details.
  */
 
-#include <linux/gk20a.h>
-
 #include <linux/version.h>
 
 #include <nvgpu/semaphore.h>