nvgpu: Fix include paths for in-tree builds

When compiling the kernel with an O= option (which stores built files
outside the source tree) the kernel adds various extra source paths to the
system include path. However, this doesn't happen when building in-tree.
Adjust the main nvgpu Makefile to ensure all required paths are part of
the system include path so that all headers can be found.

Bug 1978388

Change-Id: I51ffc78b3863b89ebb5f051c963a8016258534a3
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1544320
(cherry picked from commit 572c509152 in rel-28)
Reviewed-on: https://git-master.nvidia.com/r/1545675
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bo Yan <byan@nvidia.com>

drivers/gpu/nvgpu/Makefile.nvgpu

@@ -1,6 +1,7 @@
 GCOV_PROFILE := y
 
 ccflags-y += -I$(srctree)/../nvgpu/drivers/gpu/nvgpu/include
+ccflags-y += -I$(srctree)/../nvgpu/drivers/gpu/nvgpu
 ccflags-y += -I$(srctree)/../nvgpu/include
 ccflags-y += -I$(srctree)/../nvgpu/include/uapi