[BISECTED REGRESSION] b43legacy broken on G4 PowerBook

[Aaro Koskinen]

Hi,

When upgrading from v5.0 -> v5.1 on G4 PowerBook, I noticed WLAN does
not work anymore:

[   42.004303] b43legacy-phy0: Loading firmware version 0x127, patch level 14 (2005-04-18 02:36:27)
[   42.184837] b43legacy-phy0 debug: Chip initialized
[   42.184873] b43legacy-phy0 ERROR: The machine/kernel does not support the required 30-bit DMA mask

The same happens with the current mainline.

Bisected to:

	commit 65a21b71f948406201e4f62e41f06513350ca390
	Author: Christoph Hellwig <hch at lst.de>
	Date:   Wed Feb 13 08:01:26 2019 +0100

	    powerpc/dma: remove dma_nommu_dma_supported

	    This function is largely identical to the generic version used
	    everywhere else.  Replace it with the generic version.

	    Signed-off-by: Christoph Hellwig <hch at lst.de>
	    Tested-by: Christian Zigotzky <chzigotzky at xenosoft.de>
	    Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

A.