Pull up following revision(s) (requested by skrll in ticket #599):

sys/arch/arm/broadcom/bcm283x_platform.c: revision 1.34 (patch)

Provide a single generic bcm283x_platform_uart_freq which checks for
"brcm,bcm2835-aux-uart" and returns the appropriate core clock based
results; otherwise it returns the uart clock from firmware.

Should fix early console output on the rpi0w.

Based on a diff from mlelstv

(martin)