arm: dts: k3-j721e-r5-sk: Update R5 DT to pick the new DDR config

A new lpddr4 configuration is introduced for J7 SK with 4266 MTs data
rate. Therefore, update the R5 DTS file to point to the new DDR config
file.

Signed-off-by: Sinthu Raja <sinthu.raja@ti.com>