am437x: Add am57xx_evm_defconfig using CONFIG_DM

Import various DT files for am57xx-beagle-x15 from
Linux Kernel v4.2
Add config file for this board, enable DM, DM_GPIO,
DM_SERIAL and DM_MMC.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index 23939b0..ddc6a05 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -76,6 +76,7 @@
 	socfpga_cyclone5_sockit.dtb			\
 	socfpga_cyclone5_socrates.dtb
 dtb-$(CONFIG_TARGET_DRA7XX_EVM) += dra72-evm.dtb dra7-evm.dtb
+dtb-$(CONFIG_TARGET_BEAGLE_X15) += am57xx-beagle-x15.dtb
 dtb-$(CONFIG_TARGET_STV0991) += stv0991.dtb
 
 dtb-$(CONFIG_LS102XA) += ls1021a-qds.dtb \