ARM: DRA7: Add macros for voltage values for all OPPs

Define specific macros for the voltage values for all voltage
domains for all applicable OPPs - OPP_NOM, OPP_OD and OPP_HIGH.
No separate macros are defined for VD_MPU and VD_CORE at OPP_OD
and OPP_HIGH as these use the same values as OPP_NOM.

The current macros will be used as common macros that can be
redefined appropriately based on a selected OPP configuration
at build time.

Signed-off-by: Suman Anna <s-anna@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>