regulator: anatop: Add support for "anatop-enable-bit"

Add code to support support for "anatop-enable-bit" device-tree
property. This property translates to LINREG_ENABLE bit in real hardware
and is present on 1p1, 2p5 and 3p0 regulators on i.MX6 and 1p0d regulator
on i.MX7.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>