OMAP: hwmod: Handle opt clocks node using clk_add_alias

For every optional clock present per hwmod per omap-device, this function
adds an entry in the clocks list of the form <dev-id=dev_name, con-id=role>,
if an entry is already present in the list of the form <dev-id=NULL, con-id=role>.

The function is called from within the framework inside omap_device_build_ss(),
after omap_device_register.

This allows drivers to get a pointer to its optional clocks based on its role
by calling clk_get(<dev*>, <role>).

Link to discussions related to this patch:
http://www.spinics.net/lists/linux-omap/msg34809.html

Signed-off-by: Charulatha V <charu@ti.com>
Signed-off-by: Partha Basak <p-basak2@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[paul@pwsan.com: simplified loop iterator; removed the superfluous clk_get(),
 using the clk_get() in clk_add_alias() instead]
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Kevin Hilman <khilman@deeprootsystems.com>