firmware-brcm43752: install symlinks to fix driver loading

At some point the driver started using symlinks w/ machine IDs for finding/loading fw, and for some reason I thought it was a good idea to not install those symlinks.

Fixes this failure when loading the brcmfmac driver: brcmfmac mmc1:0001:1: Direct firmware load for brcm/brcmfmac43752-sdio.purism,librem5r4.bin failed with error -2