MAINTAINERS: Add entry for APM X-Gene SoC Ethernet (v2) driver

This patch adds a MAINTAINERS entry for the ethernet driver for
the on-chip ethernet interface which uses a linked list of DMA
descriptor architecture (v2) for APM X-Gene SoCs.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>