kbuild: rpm-pkg: add dtb files in kernel rpm

kbuild: rpm-pkg: add dtb files in kernel rpm

Some architectures, like aarch64 ones, need a dtb file to configure the
hardware. The default dtb file can be preloaded from u-boot, but the final
and/or more complete dtb file needs to be able to be loaded later from
rootfs.

Add the possible dtb files to the kernel rpm and mimic Fedora shipping
process, storing the dtb files in the module directory. These dtb files
will be copied to /boot directory by the install scripts, but add fallback
just in case, checking if the content in /boot directory is correct.

Mark the files installed to /boot as %ghost to make sure they will be
removed when the package is uninstalled.

Tested with Fedora Rawhide (x86_64 and aarch64) with dnf and rpm tools.
In addition, fallback was also tested after modifying the install scripts.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>