m68k: add amcore board support

Add Sysam Amcore m68k-based board support.

Signed-off-by: Angelo Dureghello <angelo@sysam.it>
diff --git a/configs/amcore_defconfig b/configs/amcore_defconfig
new file mode 100644
index 0000000..705c400
--- /dev/null
+++ b/configs/amcore_defconfig
@@ -0,0 +1,2 @@
+CONFIG_M68K=y
+CONFIG_TARGET_AMCORE=y