ARM: dts: imx7s-warp: Improve the Wifi description

GPIO5_10 is connected to the BCM43455 WL_REG_ON pin and it is better
descrbed via mmc-pwrseq-simple.yaml.

Also improve the Wifi devicetree description by passing a compatible
string that describes the BCM43455 presence as per brcm,bcm4329-fmac.yaml.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>