ARM: OMAP2+: hwmod: add omap_hwmod_get_resource_byname()

The timer integration code pokes around in hwmod data structures.
Those data structures are about to change.  Define a function,
omap_hwmod_get_resource_byname(), for the timer integration code to
use instead.

The original patch has been changed to use struct resource by Tony's
request, although the caller of this function should not be a driver._
Platform drivers should get their data through the regular platform_*
functions; DT drivers through the appropriate of_* functions.  This a
function is only for use by OMAP core code in arch/arm/*omap*.

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