defconfig: msm8996: enable display driver xlog debug

Enable display driver xlog debugging feature.
This feature enable: MDSS registers dump during
display driver errors, panic in major errors and
add logging of events in some key functions.
Events are logged in an internal ring buffer
and only dumped during errors.

Change-Id: I93b8cb29da812e5d6c6ebf86723bfc36f33ecce4
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>