kbuild: make binrpm-pkg always produce kernel-devel package

The generation of the kernel-devel package is disabled for binrpm-pkg
presumably because it was quite big (>= 200MB) and took a long time to
package.

Commit fe66b5d2 ("kbuild: refactor kernel-devel RPM package and
linux-headers Deb package") reduced the package size to 12MB, and now
it is quick to build. It won't hurt to have binrpm-pkg generate it by
default.

If you want to skip the kernel-devel package generation, you can pass
RPMOPTS='--without devel':

  $ make binrpm-pkg RPMOPTS='--without devel'

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>