msm: mdss: add support for RGB pipes without scalar blocks

Some MDP revisions have RGB pipes which do not have scaling
support. This change takes care of supporting those variants.
Also export this property to the userspace using the MDP
capabilities sysfs node. This will help in MDP composition
related decision making.

Change-Id: I9548bf720d5d80e0e75a71592d7394ee566dce3b
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>