APB mux.
It's larger than the AR71xx because it needs to replace the nexus
for some devices (notably wifi) and the wifi driver (if_ath_ahb.c)
reads the SPI data directly at early boot whilst it's memory mapped
in.
I'm eventually going to rip it out and replace it with a firmware
interface similar to what exists for the if_ath_pci.c path -
something early on (likely something new that I'll write) will
suck in the calibration data into a firmware API blob and that'll
be accessed from if_ath_ahb.c.
But, one thing at a time.
Tested:
* QCA955x SoC, AP135 development board
e090d1f591