meta-evb-ast2600: Add an new convenience layer for OpenBMC AST2600 EVB

This commit has been verified with AST2600A1 EVB with the image created
by the following command:

TEMPLATECONF=meta-evb/meta-evb-aspeed/meta-evb-ast2600/conf . openbmc-env
bitbake obmc-phosphor-image

Signed-off-by: Troy Lee <troy_lee@aspeedtech.com>
Change-Id: I7a3d90c8fb15a2ca8ea046b92f9cd06eb3cacd54
diff --git a/meta-evb-aspeed/meta-evb-ast2600/conf/conf-notes.txt b/meta-evb-aspeed/meta-evb-ast2600/conf/conf-notes.txt
new file mode 100644
index 0000000..9b3c01a
--- /dev/null
+++ b/meta-evb-aspeed/meta-evb-ast2600/conf/conf-notes.txt
@@ -0,0 +1,2 @@
+Common targets are:
+     obmc-phosphor-image