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/tools/Makefile b/tools/Makefile
index d49e40d..1382b05 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -156,7 +156,7 @@
 HOSTCFLAGS_ubsha1.o := -pedantic
 
 hostprogs-$(CONFIG_KIRKWOOD) += kwboot
-hostprogs-$(CONFIG_ARMADA_XP) += kwboot
+hostprogs-$(CONFIG_ARCH_MVEBU) += kwboot
 hostprogs-y += proftool
 hostprogs-$(CONFIG_STATIC_RELA) += relocate-rela