Add Portwell Neptune machine

Initial introduction of Portwell Neptune family equipped with
Aspeed 2500 BMC SoC.

Tested: Build portwell neptune board and load on the target hardware.
Ensure that BMC boots to console.

Change-Id: I7a97162dfe3031904e27f2de2691e693079c9216
Signed-off-by: Amithash Prasad <amithash@fb.com>
diff --git a/meta-portwell/meta-neptune/conf/conf-notes.txt b/meta-portwell/meta-neptune/conf/conf-notes.txt
new file mode 100644
index 0000000..9b3c01a
--- /dev/null
+++ b/meta-portwell/meta-neptune/conf/conf-notes.txt
@@ -0,0 +1,2 @@
+Common targets are:
+     obmc-phosphor-image