clk: at91: add slow clks driver

AT91 slow clk is a clk multiplexer.

In some SoCs (sam9x5, sama5, sam9g45 families) this multiplexer can
choose among 2 sources: an internal RC oscillator circuit and an oscillator
using an external crystal.

In other Socs (sam9260 family) the multiplexer source is hardcoded with
the OSCSEL signal.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

diff --cc drivers/clk/at91/Makefile
Simple merge

diff --cc drivers/clk/at91/clk-slow.c
Simple merge

diff --cc drivers/clk/at91/pmc.c
Simple merge

diff --cc drivers/clk/at91/pmc.h
Simple merge

diff --cc drivers/clk/at91/sckc.c
Simple merge

diff --cc drivers/clk/at91/sckc.h
Simple merge

diff --cc include/linux/clk/at91_pmc.h
Simple merge