clk: si570: Add a driver for SI570 oscillators

Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
The devices generate low-jitter clock signals and are reprogrammable via
an I2C interface.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

diff --cc Documentation/devicetree/bindings/clock/silabs,si570.txt
Simple merge

diff --cc drivers/clk/Kconfig
Simple merge

diff --cc drivers/clk/Makefile
Simple merge

diff --cc drivers/clk/clk-si570.c
Simple merge