ARM: dts: msm: msm8992: Add BT node, GPIO regulator

Add BT node, PMIC GPIO 18 and 19 in the device tree.

BT chip on MSM8992 board is powered via an external
regulator controlled by PM8994 GPIO 9. This external
regulator outputs a constant of 3.3 V.

Change-Id: Ibc2edad48d3c37c0e8596aafd080b36a5694f917
Signed-off-by: Bhakthavatsala Raghavendra <braghave@codeaurora.org>