kernel: rpm-pkg: Restore find-debuginfo.sh approach to -debuginfo package

kernel: rpm-pkg: Restore find-debuginfo.sh approach to -debuginfo package

Commit 62089b804895 ("kbuild: rpm-pkg: Generate debuginfo package
manually") effectively reverted commit a7c699d090a1 ("kbuild: rpm-pkg:
build a debuginfo RPM") but the approach it took is not safe for older
RPM releases. Restore commit a7c699d090a1 ("kbuild: rpm-pkg: build a
debuginfo RPM") for the !CONFIG_MODULE_SIG case to allow more
environments and configurations to take advantage of the separate debug
information package process.

Cc: stable@vger.kernel.org
Fixes: 62089b804895 ("kbuild: rpm-pkg: Generate debuginfo package manually")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>