arm64: dts: sc7180: Add a comment to i2c7 about external pullup

arm64: dts: sc7180: Add a comment to i2c7 about external pullup

Make i2c7 symmetric with the other i2c busses and comment that we have
no internal pull because there is an external one.

Reviewed-by: Rajendra Nayak <rnayak@codeaurora.org>
Fixes: ba3fc6496366 ("arm64: dts: sc7180: Add qupv3_0 and qupv3_1")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20191210163530.2.I8d4cbb3d7ac5824f8e950c53038df8c27a512905@changeid
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>