arm64: dts: msm8996: add support blsp2_uart2

This patch adds bslp2_uart2 node in soc so that boards that use this
uart can enable it.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>