Start cleaning up the voltage layer to have a voltage domain layer
that resembles the structure of the existing clock and power domain
layers. To that end:
- move the 'struct voltagedomain' out of 'struct omap_vdd_info' to
become the primary data structure.
- convert any functions taking a pointer to struct omap_vdd_info into
functions taking a struct voltagedomain pointer.
- convert the register & initialize of voltage domains to look like
that of powerdomains
- convert omap_voltage_domain_lookup() to voltdm_lookup(), modeled
after the current powerdomain and clockdomain lookup functions.
- omap_voltage_late_init(): only configure VDD info when
the vdd_info struct is non-NULL
Signed-off-by: Kevin Hilman <khilman@ti.com>