ARM: dts: mvebu: linksys: enable buffer manager support

Add appropriate properties to devices in the Linksys WRT AC Series for the
mvneta driver to use hardware buffer management.

Also update "soc" ranges property and set the status of bm and bm-bppi
to "okay" (SRAM).

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>