ARM: OMAP2+: hwmod: add function to iterate over struct omap_hwmod_ocp_if

To reduce the number of lines of data in the OMAP portion of the Linux
code base, subsequent patches will remove the lists of hwmod
interconnect links from the static hwmod data.  These lists will be
built dynamically during boot.  To ease this transition, this patch
centralizes the way that interconnect links are iterated into a single
function, _fetch_next_ocp_if().

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>