drivers: sensors: add sensors ssc driver

SLPI (sensor low power island) uses Qualcomm Digital Signal Processor
for all sensors connected via SPI/I2C. Firmware is required to be
loaded to enable these sensors and algorithms to execute on DSP.  This
change adds driver to load the firmware.

This snapshot is taken as of msm-4.4 'commit 2fdff7859789 ("clk:
qcom: Add support for throttle clocks for clients")' and minor
modifications in Documentation.

Change-Id: Idcd5cfe4d2148496833808e381324edb3dde1708
Signed-off-by: Ananda Kishore <kananda@codeaurora.org>
Signed-off-by: Punit Soni <punits@codeaurora.org>
Signed-off-by: Shaikh Shadul <sshadu@codeaurora.org>