ARM: dts: imx28-m28evk: populate fixed regulators

Fixed regulators put under "regulators" node will not be populated,
unless simple-bus or something similar is used.  Drop the "regulators"
wrapper node to fix this.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>