slimbus: ngd: Add qcom SLIMBus NGD driver

This patch adds suppor to Qualcomm SLIMBus Non-Generic Device (NGD)
controller driver.
This is light-weight SLIMBus controller driver responsible for
communicating with slave HW directly over the bus using messaging
interface, and communicating with master component residing on ADSP
for bandwidth and data-channel management

Based on intial work from
Karthikeyan Ramasubramanian <kramasub@codeaurora.org> and
Sagar Dharia <sdharia@codeaurora.org>

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Craig Tatlor <ctatlor97@gmail.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>