arm/dts: Mark vcxio, v2v1 and v1v8 regulators as always on

vcxio, v2v1 and v1v8 are expected to be always on, update the dtsi
for twl6030 to reflect this.

commit '86f5fc' regulator: core: Mark all DT based boards as having
full constraints) caused these to be disabled at late boot causing
OMAP4 boards (using twl6030) to lockup.

Reported-by: Kishon Vijay Abraham I <kishon@ti.com>
Reported-by: J Keerthy <j-keerthy@ti.com>
Signed-off-by: Rajendra nayak <rnayak@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>