drm/msm: add default value for plane enum property

Add default value support for plane enum property which caller is
able to pass in different default value when initialize the enum
property list.

Change-Id: I57595bf7c42b0e528a18ab0951655a169b00d611
Signed-off-by: Jin Li <jinl@codeaurora.org>
Signed-off-by: Yunyun Cao <yunyunc@codeaurora.org>