ARM: dts: keystone-k2l-evm: Add and enable common DSP CMA memory pool

A common CMA memory pool reserved memory node is added, and is attached
to all the DSP nodes through the 'memory-region' property on the 66AK2L
EVM board. This area will be used for allocating virtio rings and buffers.
The common node allows the DSP Memory Protection and Address Extension
(MPAX) module to be configured uniformly across all the DSP processors.

The reserved memory node and all the user DSP nodes are also marked okay
to enable the DSPs on the 66AK2L EVM board.

Signed-off-by: Sam Nelson <sam.nelson@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>