ARM: bcm2711-rpi.dts: Unlock DMA channels 9 & 10

The downstream-specific override of the 32-bit DMA mask needlessly
disables channels 9 and 10 - the VPU doesn't use them. This override
is redundant, so delete it.

See: https://github.com/raspberrypi/linux/issues/3896



Signed-off-by: Phil Elwell <phil@raspberrypi.com>