drm/msm/sde: increase max CTLs to 6

Increase the maximum supported CTL hardware blocks whose offsets are
defined by the device node qcom,sde-ctl-off to allow for up to 6
CTLs.  See the Documentation/devicetree/bindings/display/msm/sde.txt
for information on defining CTL blocks on supported chipsets.

Change-Id: I58ce98e61eb5c2314d596b18006f350deb22a6e4
Signed-off-by: Steve Cohen <cohens@codeaurora.org>