gpu: nvgpu: Set default large page size to 64K for gm20b

Since all userspace apps are using 64K pages these days it makes
sense to set the default large page size to 64K. This in turn
causes the PDE coverage field to be set to 64M in the GPU
characteristics field.

While it would therefor be possible to create a VM with a PDE
coverage that's larger than 64M (128M if you set the large
page size to 128K) this will make the defaults work properly.
This in turn fixes a CUDA issue where CUDA tries to determine
the PDE coverage (and correspondingly a minimum alignemnt) from
the characteristics IOCTL.

Bug 200105199

Change-Id: Iee3c213f1b81d8628571f46c7ad5e16fbfe07499
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1781088
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/gm20b/mm_gm20b.c

@@ -58,7 +58,7 @@ u32 gm20b_mm_get_big_page_sizes(void)
 
 u32 gm20b_mm_get_default_big_page_size(void)
 {
-	return SZ_128K;
+	return SZ_64K;
 }
 
 bool gm20b_mm_support_sparse(struct gk20a *g)