disp: msm: specify default value for msm enum property

Allow caller to specify the default value of the enum
property while installing with msm prop layer. It is
not always the case that the default value to be the
first entry.

Change-Id: Ie0bb1ad7479e3e07810b3d817fdf618b1935858c
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>