clk: nomadik: move src init out of nomadik_clk_init

nomadik_clk_init currently also maps system reset controller base address
used by clocks and registers a reboot notifier. To allow further cleanup of
nomadik clk setup, this moves system reset controller setup from
nomadik_clk_init to its own function.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Mike Turquette <mturquette@linaro.org>