clk: wrap I/O access for improved portability

the common clock drivers were motivated/initiated by ARM development
and apparently assume little endian peripherals

wrap register/peripherals access in the common code (div, gate, mux)
in preparation of adding COMMON_CLK support for other platforms

Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

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

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

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

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