[RPM] Add virtual conf package
Add virtual conf package to resolve build dependency issue as suggested
in https://github.com/nnstreamer/api/pull/21#issuecomment-
804599118
With this patch, it is now possible to install devel package with
`/etc/nntrainer.ini` or the packager choose to use `test-devel` when
building.
See also nnstreamer/nntrainer#1034
**Evaluation Method**
Cross building with nntrainer package
**Self evaluation:**
1. Build test: [X]Passed [ ]Failed [ ]Skipped
2. Run test: [X]Passed [ ]Failed [ ]Skipped
Cc: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Jihoon Lee <jhoon.it.lee@samsung.com>