gpu: nvgpu: gk20a: always map ptes for 64 bit arch

gpu: nvgpu: gk20a: always map ptes for 64 bit arch

On 64 bit architecture, we have plenty of vmalloc space
so that we can keep all the ptes mapped always
But on 32 but architecture, vmalloc space is limited and
hence we have to map/unmap ptes when required

Hence add new APIs for arch64 and call them if
IS_ENABLED(CONFIG_ARM64) is true

Bug 1443071

Change-Id: I091d1d6a3883a1b158c5c88baeeff1882ea1fc8b
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/387642
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>