ARM: dts: DRA7: Add CPU OPP table

Add DT OPP table for DRA7xx family of devices. This data is decoded by
OF with of_init_opp_table() helper function.

The data is based on DRA75x, DRA74x Data Manual revision F (Sept 2013).

TODO: add OPP_HIGH after AVS-Class0 is functional
NOTE: The voltage and frequency values work well only on NOM samples
and it is mandatory to use ABB/AVS Class 0 support for all OPPs.

Clock nodes are pending clock node alignment.

[nm@ti.com: cleanups and rebase to latest]
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: J Keerthy <j-keerthy@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>