ARM: dts: msm: Add extcon phandle for usb_qmp_dp_phy for sdmmagpie

This change adds extcon phandle for usb_qmp_dp_phy which
is used by driver for notifying number of lanes in case of
USB+DP concurrent mode.

Change-Id: I2a762f231c35c4723d65cf351bf59a5e41304e4a
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>