msm: dcvs: fail gracefully if TZ does not support dcvs

If dcvs attempts to initialize on a system where TZ does not support
dcvs, it will eventually cause a crash. Prevent this by disabling
dcvs if TZ does not successfully initialize its part of dcvs.

Change-Id: Ic9cd361243c03c3832133614c4847a2815b0bbb4
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>