ARM: dts: ls1021a: remove regulators simple-bus

There is no regulator bus in hardware.  So move the regulator nodes out
and remove the regulators simple-bus.  This also make the dts align with
the simple-bus schema.

Signed-off-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>