ramips: ZTE-Q7: fix switch driver initialization in DTS (FS#716)

Add the changes suggested by FS#716 to fix the switch driver initialization
on the ZTE Q7.

Also remove the `pinctrl-names` field obsoleted by the changes.

Reported-by: Harry Lau <harrylwc@gmail.com>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>