msm: mdss: fix single layer calculation during PREPARE IOCTL

BW calculations of display controller depends on how many pipes are
staged on a given layer mixer (LM). Currently BW calculations are done
twice, once during PREPARE IOCTL to check if BW is within system defined
limits and other during commit IOCTL. During both calculations, we need
to find out how many pipes are staged on a give LM. When these
calculations are done during frame (n)'s PREPARE IOCTL, frame (n-1)'s
pipe stage information is used rather than frame (n)'s. This can lead to
false BW checks in PREPARE IOCTL and allows display controller with
configuration beyond its BW limits. Fix this by propagating frame (n)'s
intended number of staged pipes to BW calculation function.

Change-Id: I7561f6b020dc46ca356efac3f690bda1eb810ca4
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>