arm64: tegra21: emc: Make sure the DLL always has a clock

arm64: tegra21: emc: Make sure the DLL always has a clock

Ensure the DLL always has a clock. If it does not then the DLL will
not be able to swap to a new clock source. That is to say the DLL
requires both the old and new clock source to be active when its
source is changed.

Bug 1655375

Change-Id: I796725b95628d7ea6753d7986af74324e9c1489b
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/1152001
(cherry picked from commit e0a23c1f4a99a88b09faedd82dbdba64fc138bec)
Reviewed-on: http://git-master/r/1185062
GVS: Gerrit_Virtual_Submit
Tested-by: Robert Collins <rcollins@nvidia.com>
Reviewed-by: Akhilesh Khumbum <akhumbum@nvidia.com>
Reviewed-by: Robert Collins <rcollins@nvidia.com>