ARM: OMAP: omap_device: Add omap_device_get_by_hwmod_name

ARM: OMAP: omap_device: Add omap_device_get_by_hwmod_name

An API which translates a standard hwmod name to corresponding
platform_device is useful for drivers when they need to look up the
device associated with a hwmod name to map back into the device
structure pointers. These ideally should be used by drivers in
mach directory. Using a generic hwmod name like "gpu" instead of
the actual device name which could change in the future, allows
us to:
a) Could in effect help replace apis such as omap2_get_mpuss_device,
omap2_get_iva_device, omap2_get_l3_device, omap4_get_dsp_device,
etc..
b) Scale to more devices rather than be restricted to named functions
c) Simplify driver's platform_data from passing additional fields
all doing the same thing with different function pointer names
just for accessing a different device name.

Signed-off-by: Nishanth Menon <nm@ti.com>
[b-cousson@ti.com: Adapt it to the new pdev pointer inside od,
remove the unneeded helpers, and fold the next patch here]
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>