clk: prima2: declare OF clock provider

Common clock framework allows to register clock providers to get called
on of_clk_init() by using CLK_OF_DECLARE. This converts prima2 clock
provider to make use of it and get rid of the mach specific clk init
call.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Barry Song <baohua.song@csr.com>
Acked-by: Mike Turquette <mturquette@linaro.org>