MFC r336623 by mmacy:

Fixes the interrupt storm in UART during the boot on ARMADA38X. The missing
attribution of ns8250->busy_detect breaks the UART support.

Original commit log:

Add busy detect quirk to list of console options

This change allows one to set the busy_detect flag
required by the synopsys UART at the loader prompt.
This is needed by the EPYC 3000 SoC.

This will give users a working console up to the point where getty is required:
hw.uart.console="mm:0xfedc9000,rs:2,bd:1"

Sponsored by: Rubicon Communications, LLC (Netgate)