ARM: dts: imx6qdl-hummingboard2: add v1.5 som without eMMC

Add support for the v1.5 SOM with TI Wi-Fi but without eMMC.  As the
pinmux settings are different for the microsom, we need to use a
separate board-level dts for this as there is no support for overlays.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>