video: tegra: host: g20a: Add AELPG feature

video: tegra: host: g20a: Add AELPG feature

Add basic functionality and helper routines for AELPG. Also,
enable AELPG during init.

Enabling adaptive elpg is needed for the data corruption
issues seen as per the bug reported below.
Bug 1458353

Change-Id: Ie6effc354dc1ade2a4baa2585984ff39d7c0660d
Signed-off-by: Prashant Malani <pmalani@nvidia.com>
Reviewed-on: http://git-master/r/338873
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>
(cherry picked from commit 2b235e3708857f12ee765a85ce7a61cc464ac98e)
Signed-off-by: Prabhu Kuttiyam <pkuttiyam@nvidia.com>
Reviewed-on: http://git-master/r/394410
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Winnie Hsu <whsu@nvidia.com>