Platform/Raspberrypi: Update DMA constants based on SOC revision

The newer BCM2711 SoC's don't have a DMA constraint on the emmc2
controller. So we don't need to do the 1G translation. Lets
allow the AML to detect the SoC revision and return a different
_DMA resource.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Pete Batard <pete@akeo.ie>