automation: Linux 5.10.74 test-artifact

automation: Linux 5.10.74 test-artifact

Build a 5.10 kernel to be used as Dom0 and DomU kernel for testing. This
is almost the same as the existing ARM64 recipe for Linux 5.9, the
only differences are:
- upgrade to latest 5.10.x stable
- force Xen modules to built-in (on ARM it was already done by defconfig)

Also add the exporting job to build.yaml so that the binary can be used
during gitlab-ci runs.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>