ARM: dts: bcm6846: Add ARM PL081 DMA block

ARM: dts: bcm6846: Add ARM PL081 DMA block

The ARM PL081 DMA controller can be found in the BCM6846
memory map, and it turns out to work.

The block may be used as DMA engine for some of the
peripherals (maybe the EMMC controller found in the same
group of peripherals?) but it can always be used as a
memcpy engine, which is a generic "blitter".

I tested it with the dmatest module, and it copies
lots of data very fast and fires hundreds of thousands
of interrupts so it works just fine.

Add it to the BCM6846 DTSI file.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20241019-genexis-xg6846b-base-v3-6-8375a0e1f89f@linaro.org
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>