AST2400: Set u-boot preferred provider version

In preparation for supporting AST2500 with a different branch.

Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/meta-ast2400/conf/machine/include/ast2400.inc b/meta-ast2400/conf/machine/include/ast2400.inc
index 964de9a..8510a03 100644
--- a/meta-ast2400/conf/machine/include/ast2400.inc
+++ b/meta-ast2400/conf/machine/include/ast2400.inc
@@ -4,6 +4,8 @@
 
 PREFERRED_PROVIDER_virtual/kernel ?= "linux-obmc"
 PREFERRED_VERSION_linux-obmc ?= "4.4+git%"
+PREFERRED_VERSION_u-boot ?= "v2013.07+git%"
+PREFERRED_VERSION_u-boot-fw-utils ?= "v2013.07+git%"
 
 UBOOT_MACHINE ?= "palmetto_config"
 UBOOT_ENTRYPOINT ?= "0x40001000"