ARM: dts: BT: Add support for UART clock

BT host to controller communication happens through UART. UART is
enabled in dtsi. This provides BT HOST to vote on/off for UART clock.

Change-Id: Ie7bf2607c37efa13b33e4cfe5eda9f934c281e37
Signed-off-by: Lakshmi Pola <ppriyank@codeaurora.org>
Signed-off-by: Bhasker Reddy Komatireddy <kbhasker@codeaurora.org>