ARM: dts: msm: add display wb linewidth property to sdm845

Add display writeback linewidth property to mdss mdp node.
This property specifies the maximum line width of writeback.
Without this property, writeback line width will be limited
to default value, which is smaller than the value supported
by sdm845.

CRs-Fixed: 2009714
Change-Id: I7138cb3fe8a790825fc7b2eee6580eac899bbb22
Signed-off-by: Alan Kwong <akwong@codeaurora.org>