dt-bindings: FEC/i.MX DWMAC and INTMUX maintainer

Emails to Joakim Zhang bounce, add Shawn Guo (i.MX architecture
maintainer) and the NXP Linux Team exploder email as well as well Wei
Wang for FEC and Clark Wang for DWMAC.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>