kernel: fitimage: basic support for fitimage signature
This is an initial support of fitImage signature to enable U-Boot verified
boot. This feature is implemented by adding a signature tag to the
configuration section of the generated fit-image.its file.
When a UBOOT_SIGN_ENABLE variable is set to "1", the signature procedure is
activated and performs a second call to mkimage to sign the fitImage file and
to include the public key in the deployed U-Boot device tree blob. (This
implementation depends on the use of CONFIG_OF_SEPARATE in U-Boot.)
As the U-Boot device tree blob is appended in the deploy dir, a dependency
on 'u-boot:do_deploy' is added when the feature is activated.
Signed-off-by: Yannick Gicquel <yannick.gicquel@iot.bzh> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
