arm: mvebu: Add armada-xp-maxbcm.dts for maxbcm board

This is needed for the upcoming ethernet DM conversion of the maxbcm
board. The configuration of the PHY is then extracted from the DT
instead of using the defines from the config header.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
diff --git a/configs/maxbcm_defconfig b/configs/maxbcm_defconfig
index 7506fbf..200c7a0 100644
--- a/configs/maxbcm_defconfig
+++ b/configs/maxbcm_defconfig
@@ -2,7 +2,7 @@
 CONFIG_ARCH_MVEBU=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_TARGET_MAXBCM=y
-CONFIG_DEFAULT_DEVICE_TREE="armada-xp-gp"
+CONFIG_DEFAULT_DEVICE_TREE="armada-xp-maxbcm"
 CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set