msm: mdss: add property to set from device tree the overlap BW fudge factor

Current calculations apply one fudge factor to the final bandwidth
regardless if this is a result from the overlap or prefill calculation.
With this change the final bandwidth can be tuned up to apply a different
fudge factor when the bandwidth depends on the overlap calculation.

CRs-Fixed: 635005
Change-Id: Iaa9718bda3264a47bf70a2facba0d23e4b2414f3
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>