net: ethernet: ti: add lkml version of dma descriptors pool

commit 93a76530 upstream.

Add lkml version of dma descriptors pool to sync MCU CPSW code to LKML
version as max as possible. Used initial LKML commit to identify that code
already upstream.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>