video: tegra: nvmap: Add ref count in nvmap_vma_list

video: tegra: nvmap: Add ref count in nvmap_vma_list

Add ref count to prevent invalid vma removal from the h->vmas list
and also allow addition of a different vma which also has same
nvmap_vma_priv as vm_private_data into the h->vmas list. Both cases
are allowed in valid usage of nvmap_vma_open/nvmap_vma_close.

Bug 200164002

Change-Id: Ifc4d281dd91e1d072a9a3ee85e925040bd65a6bc
Signed-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Signed-off-by: Bryan Wu <pengw@nvidia.com>
Reviewed-on: http://git-master/r/1133708
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>