msm: mdss: Fix CSC programming for VIG3 pipe

CSC programming assumes that pipe numbers are symmetric for same
type. This assumption is not valid with APQ8084 and leads to skipping
of CSC programming for VIG3 pipe. Fix this by using helper APIs to
find out if pipe is VIG or not rather than directly manipulating data
structures.

Change-Id: I130ee3994d1f5c5a96e644f8095c75d2189fbdda
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>