ARM: dts: dra7-evm: Keep all VDD rails always-on

DRA7 Data Manual (SPRS857L - August 2014) section 4.1.1 states: "All
unused power supply balls must be supplied with the voltages specified
in the Section 5.2, Recommended Operating Conditions".

This implies that all unused voltage rails for Vayu can never be
switched off even if the hardware blocks inside that voltage domain is
unused. Switching off these unused rails may result in stability issues
on other domains and increased leakage and power-on-hour impacts.

J6eco-evm dts file already considers this, however j6evm-dts file needs
to be fixed to consider this constraint of the SoC.

Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>