u-boot fw-utils: Add alternate fw_env config

Allows fw_setenv/fw_printenv tools to access alternate bmc image.

Change-Id: I7f634fd1201f5df1af01f4407d9d8791557242ae
Signed-off-by: Edward A. James <eajames@us.ibm.com>
diff --git a/meta-ast2500/recipes-bsp/u-boot/u-boot_%.bbappend b/meta-ast2500/recipes-bsp/u-boot/u-boot_%.bbappend
index f214b22..ae77edd 100644
--- a/meta-ast2500/recipes-bsp/u-boot/u-boot_%.bbappend
+++ b/meta-ast2500/recipes-bsp/u-boot/u-boot_%.bbappend
@@ -1,3 +1,4 @@
 FILESEXTRAPATHS_prepend_ast2500 := "${THISDIR}/files:"
 
 SRC_URI_append_ast2500 = " file://fw_env.config"
+SRC_URI_append_ast2500 += "file://alt_fw_env.config"