apm821xx: add amcc, usb-otg-405ex devicetree definition

This patch adds support for the amcc,usb-otg-405ex device
which is found in all APM82181 SoCs.
Note: The system can't use the generic "snps,dwc2" compatible
because of the special ahbcfg configuration. The default
GAHBCFG_HBSTLEN_INCR4 of snps,dwc2 can cause a system hang
when the USB and SATA is used concurrently.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>