aspeed: Add AST2600 platform support

Add low level platform initialization for the AST2600 SoC.
The 2-stage booting with U-Boot SPL are leveraged to support
different booting mode.

However, currently the patch supports only the booting from
memory-mapped SPI flash.

Signed-off-by: Chia-Wei, Wang <chiawei_wang@aspeedtech.com>
Reviewed-by: Ryan Chen <ryan_chen@aspeedtech.com>
diff --git a/board/aspeed/evb_ast2600/Makefile b/board/aspeed/evb_ast2600/Makefile
new file mode 100644
index 0000000..9291db6
--- /dev/null
+++ b/board/aspeed/evb_ast2600/Makefile
@@ -0,0 +1 @@
+obj-y += evb_ast2600.o