ARM: dts: imx6q-pico: fix board compatibles

There are four flavors of TechNexion PICO-IMX6 boards.  They have their
own DTSes, even though in Dwarf, Nymph and Pi are exactly the same.
They also have their own bindings so adjust the compatibles to match the
bindings.

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