ARM: dts: dra7-evm: Make VDDA_1V8_PHY supply always on

After clarification from the hardware team it was found that
this 1.8V PHY supply can't be switched OFF when SoC is Active.

Since the PHY IPs don't contain isolation logic built in the design to
allow the power rail to be switched off, there is a very high risk
of IP reliability and additional leakage paths which can result in
additional power consumption.

The only scenario where this rail can be switched off is part of Power on
reset sequencing, but it needs to be kept always-on during operation.

This patch is required for proper functionality of USB, SATA
and PCIe on DRA7-evm.

CC: Rajendra Nayak <rnayak@ti.com>
CC: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>