msm_fb: display: mdp4 version assigned at board file

Currently, mdp version is acquired by reading mdp version
register. This patch use mdp version from board file instead
of reading from mdp register.

Change-Id: If71be4f28caa45beea58789ca1025a338eb64de5
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>