meta-aspeed: Add development key for Kernel sign

Add a development (insecure, also known as 'imprint') key to
linux-aspeed that can be used for signing the Kernel fitImage
for U-Boot FIT Signature Verification.

The key was generated according to U-Boot documentation, using:
  $ openssl genpkey -algorithm RSA -out rsa_oem_fitimage_key.key \
        -pkeyopt rsa_keygen_bits:4096 -pkeyopt rsa_keygen_pubexp:65537

The certificate was created according to U-Boot documentation, using:
  $ openssl req -batch -new -x509 -key rsa_oem_fitimage_key.key \
        -out rsa_oem_fitimage_key.crt

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
Change-Id: Ic67024ab389c8a4a3fc6709e1d7d92dc72783ca5
diff --git a/meta-aspeed/recipes-kernel/linux/linux-aspeed.inc b/meta-aspeed/recipes-kernel/linux/linux-aspeed.inc
index 6a1471f..aa06029 100644
--- a/meta-aspeed/recipes-kernel/linux/linux-aspeed.inc
+++ b/meta-aspeed/recipes-kernel/linux/linux-aspeed.inc
@@ -8,7 +8,11 @@
 
 KSRC ?= "git://github.com/openbmc/linux;protocol=git;branch=${KBRANCH}"
 SRC_URI = "${KSRC}"
-SRC_URI += " file://defconfig"
+SRC_URI += " \
+             file://defconfig \
+             file://rsa_oem_fitimage_key.key;sha256sum=eeb4ff2ebbfbd97b6254fe6dbaeea41067e54c65176c233ec7b2ab2decf1ddcd \
+             file://rsa_oem_fitimage_key.crt;sha256sum=45f5a55497cce8040999bf9f3214d471ac7b83ab7acef41c4425a34662e8372e \
+           "
 
 LINUX_VERSION_EXTENSION ?= "-${SRCREV}"