muge: update FDT LED configuration

Also use LED mode settings from the FDT to set the PHY.
From v3 of the patch submitted in the PR.

I moved the sc_led_modes and sc_led_modes_mask default setting outside
of the #ifdef FDT case.

PR: 237325
Submitted by: Ralf <iz-rpi03@hs-karlsruhe.de>
Reviewed by: ian
MFC after: 2 weeks
MFC with: r348001
Event: Waterloo Hackathon 2019
Differential Revision: https://reviews.freebsd.org/D20325