MAINTAINERS: Remove DT bindings area

Now that the dts/bindings filter has been removed from
Devicetree Binding area, this area serves no real purpose.

Move the include/dt-bindings files to their respective areas.

Fix some of the orphaned dts/bindings paths.

Add regex filter for any binding with "zephyr" in the name to be
in the devicetree area.

Fix the imx_spc.h file being in it's own pm/ folder instead of
power/ like the other power related headers.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>