ARM: Tegra: Omit L2 flush at disable

In Tegra kernel L2 is disabled only upon CPU cluster power down,
e.g. LP2 entry. Flushing L2 upon every LP2 entry is costly.
Since we are always in single core mode upon cluster power down
we can safely omit L2 flush upon L2 disable.

Change-Id: I27542b11e6133f3192a02440e5b14ea408b860fd
Signed-off-by: Antti P Miettinen <amiettinen@nvidia.com>
Reviewed-on: http://git-master/r/105625
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Aleksandr Frid <afrid@nvidia.com>
Reviewed-by: Diwakar Tundlam <dtundlam@nvidia.com>