cpufreq: ti-cpufreq: omap36xx use "cpu0","vbb" if run in multi_regulator mode

In preparation for using the multi_regulator capability of
this driver for handling the ABB LDO for OPP1G of the omap36xx
we have to take care that the (legacy) vdd-supply name is
cpu0-supply = <&vcc>;

To do this we add another field to the SoC description table which
optionally can specify a list of regulator names.

For omap36xx we define "cpu0-supply" and "vbb-supply".

The default remains "vdd-supply" and "vbb-supply".

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>