drivers: Enable -Wmissing-prototypes

The compiler option -Wmissing-prototypes is being enabled globally in
the upstream Linux kernel and this causes build failures for various
drivers. The build failures occur because either the driver is missing
an include file which has the prototype or because the function is not
declared statically when it should be (ie. there are no external users).

Fix the various build failures and enable -Wmissing-prototypes to
prevent any new instances from occurring. Note that the only driver that
is not fixed at the moment is rtl8822ce due to large number of failures
and so build this with '-Wno-missing-prototypes' for now, which is not
different to how it was being compiled prior to this change.

Bug 4404965

Change-Id: Ie5572d23659e0346fa035d645d9043b0a6da5fdc
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/3027488
(cherry picked from commit d5391a25ab)
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/3034644
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>

drivers/gpu/drm/tegra/drm.c

@@ -26,6 +26,7 @@
 #include <drm/drm_ioctl.h>
 #include <drm/drm_prime.h>
 #include <drm/drm_vblank.h>
+#include <drm/tegra_drm-next.h>
 
 #if IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)
 #include <asm/dma-iommu.h>

drivers/gpu/host1x/cdma.c

@@ -496,7 +496,7 @@ resume:
 	host1x_hw_cdma_resume(host1x, cdma, restart_addr);
 }
 
-void cdma_update_work(struct work_struct *work)
+static void cdma_update_work(struct work_struct *work)
 {
 	struct host1x_cdma *cdma = container_of(work, struct host1x_cdma, update_work);