ptm: tegra210: support scatter-gather for etr

ptm: tegra210: support scatter-gather for etr

To eliminate the need for fixed carveout for PTM, use scatter-gather
mode for ETR. Memory is allocated when ETR is enabled, freed when it
is disabled.

bug 1603640

Change-Id: Id6b5357055836075bad425a6380c4a457d88a9a1
Signed-off-by: Bo Yan <byan@nvidia.com>
Reviewed-on: http://git-master/r/677502
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Mitch Luban <mluban@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>