virtualization/linux-yocto: For kernel metadata use git repository instead of local...

virtualization/linux-yocto: For kernel metadata use git repository instead of local files.

This will allow using branches for supporting multiple kernel versions
more easily.

Note, that BSP description root file virtio-aarch64-standard.scc has to
be kept local withing a recipe. This is needed to add this scc file
explicitly to SRC_URI to have AGL VIRTIO patches applied during kernel
recipe build.

As explained in [1, 2], Yocto kernel metadata is commonly used for two
purposes:

1. To construct Yocto kernel git by committing patches listed in scc
files.
2. To configure Yocto kernel during Yocto build.

When scc file is not explicitly added to SRC_URI, then patch commands
will be ignored during Yocto build because it is assumed that patches
are already pre-applied during Yocto kernel git tree construction.

But, there is not AGL Linux kernel tree, only a repository for AGL
kernel metadata (this one). So, patches from this metadata repository
have to be applied during kernel recipe build.

On the other hand, to ignore patches from YP kernel metadata (which are
already pre-applied), standard.scc is included with `nopatch` keyword.

[1]: https://www.yoctoproject.org/pipermail/yocto/2019-October/046986.html
[2]: https://docs.yoctoproject.org/kernel-dev/maint-appx.html

Bug-AGL: SPEC-4452
Change-Id: Idde8e507eb18fa26e6a5b84ab8443576badb58bf
Signed-off-by: Vasyl Vavrychuk <vasyl.vavrychuk@opensynergy.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/27878
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>