soc: qcom: bgcom_dev: add user interface for BGCOM communication

This driver provide a bg_com_dev char device to act as communication
channel between user space application and kernel space BGCOM layer.
BGCOM interface handles request to access Blackghost hardware in
the device. Blackghost is a companion chip to perform low power task.

Change-Id: I07b506a6084e4b1c1b6c1179e29da63d4a6a0ef5
Signed-off-by: Pranshu Gupta <pransh@codeaurora.org>