gpu: nvgpu: extract priv cmdbuf from channel.c

Move private command buffer related functionality to priv_cmdbuf.c. This
is used only for kernel mode submits, so it makes sense to group it out,
and the priv cmdbuf stuff is used also by things that don't care about
channels.

Jira NVGPU-4548

Change-Id: Idbb42e3ed3984e16c654bb9aa2b7564b780048a4
Signed-off-by: Konsta Hölttä <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2323146
(cherry picked from commit bb67bfc7ab8e87236f31bc4f6c80dab042609f21)
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2328406
Reviewed-by: automaticguardword <automaticguardword@nvidia.com>
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-misra <svc-mobile-misra@nvidia.com>
Reviewed-by: svc-mobile-cert <svc-mobile-cert@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/sync/channel_sync_semaphore.c

@@ -35,6 +35,7 @@
 #include <nvgpu/channel.h>
 #include <nvgpu/channel_sync.h>
 #include <nvgpu/channel_sync_semaphore.h>
+#include <nvgpu/priv_cmdbuf.h>
 #include <nvgpu/fence.h>
 
 #include "channel_sync_priv.h"

drivers/gpu/nvgpu/common/sync/channel_sync_syncpt.c

@@ -34,6 +34,7 @@
 #include <nvgpu/channel.h>
 #include <nvgpu/channel_sync.h>
 #include <nvgpu/channel_sync_syncpt.h>
+#include <nvgpu/priv_cmdbuf.h>
 #include <nvgpu/fence.h>
 #include <nvgpu/string.h>