msm: mdss: fix issue of overlapping BW for two adjacent surfaces

Current code detects two adjacent surfaces as if those were overlapping,
this can impact by increasing the bandwidth calculations in this scenario.
These changes correct the algorithm to avoid the overlap in boundaries
that are only adjacent.

Change-Id: Iee43c1662c90c38dbff03991ee93884ef444fb19
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>