ARM: OMAP: clock: Define a function to enable clocks at init

Platform code can use omap2_clk_enable_init_clocks() to enable a
list of clocks that are needed to be enabled at init.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Mike Turquette <mturquette@ti.com>
[paul@pwsan.com: added kerneldoc to non-trivial new function]
Signed-off-by: Paul Walmsley <paul@pwsan.com>