msm: mdss: update split fb for HDMI usecases

For HDMI usecases, set the correct split_mode and split_fb
values on resolution change. Previously, HDMI resolution switch
within the same split_mode was not updating the split_fb values.
Update the mode and values according to the new resolution.

Change-Id: I56d0d937056a1aeff114d6addd674287b202ee60
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>