dts: imx8mq-librem5: usb_dwc3_1: Limit to USB 2.0

2 jobs for usb2 in 68 minutes and 20 seconds (queued for 2 seconds)
latest
Status Name Job ID Coverage
  Build
passed build:aarch64 #361896
librem5

00:34:14

passed build:deb #361897
librem5:arm64

01:08:20