ARM: highbank: remove custom .init_time hook

With arch/arm calling of_clk_init(NULL) from time_init(), we can now
remove custom .init_time hooks. Highbank clock provider need a reference
to system registers, as a workaround current clk driver maps those
independent of arch code now.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Mike Turquette <mturquette@linaro.org>