ARM: dts: qcom: add gsbi7 serial to ipq8064 SoC device tree

The gsbi_serial7 under gsbi7 is used by the IPQ8068 based board EWS870AP as
main serial console.

Signed-off-by: Sven Eckelmann <sven.eckelmann@openmesh.com>
Signed-off-by: Andy Gross <andy.gross@linaro.org>