drm/msm: return kms structure from helper function

Kms was being populated in a helper function, but it was
returning NULL. This change changes the helper function
to return the kms pointer. This also splits the init functin
into helper functions to address CCN threshold.

Change-Id: I8825d013d87b1803953404a65c14927e0951046f
Signed-off-by: Samantha Tran <samtran@codeaurora.org>