arm: mvebu: Move SoC selection (A38X vs AXP) into Kconfig

Until now, the SoC selection for the ARCH_MVEBU platforms has been done
in the config header. Using CONFIG_ARMADA_XP in a non-clear way. As
it needed to get selected for AXP and A38x based boards. This patch
now changes this to move the SoC selection to Kconfig. And also
uses CONFIG_ARCH_MVEBU as a common define for both AXP and A38x.
This makes things a bit clearer - especially for new board additions.

Additionally the defines CONFIG_SYS_MVEBU_DDR_AXP and
CONFIG_SYS_MVEBU_DDR_A38X are replaced with the already available
CONFIG_ARMADA_38X and CONFIG_ARMADA_XP.

And CONFIG_DDR3 is removed, as its not referenced anywhere.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
diff --git a/drivers/Makefile b/drivers/Makefile
index c9031f2..00da40b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -14,8 +14,8 @@
 obj-$(CONFIG_SPL_GPIO_SUPPORT) += gpio/
 obj-$(CONFIG_SPL_MMC_SUPPORT) += mmc/
 obj-$(CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT) += ddr/fsl/
-obj-$(CONFIG_SYS_MVEBU_DDR_A38X) += ddr/marvell/a38x/
-obj-$(CONFIG_SYS_MVEBU_DDR_AXP) += ddr/marvell/axp/
+obj-$(CONFIG_ARMADA_38X) += ddr/marvell/a38x/
+obj-$(CONFIG_ARMADA_XP) += ddr/marvell/axp/
 obj-$(CONFIG_ALTERA_SDRAM) += ddr/altera/
 obj-$(CONFIG_SPL_SERIAL_SUPPORT) += serial/
 obj-$(CONFIG_SPL_SPI_FLASH_SUPPORT) += mtd/spi/