tizen: Export kernel-devel's package version as %kernel_devel_uname_r

tizen: Export kernel-devel's package version as %kernel_devel_uname_r

This macro provides full version string of available kernel headers
as provided by kernel-devel package.

This functionality should simplify process of packaging additional
external kernel modules eliminating the step of manual searching
for appropriate kernel build directory, eg.

  BuildRequires: kernel-devel

  %build
  make M=/lib/modules/%{kernel_devel_uname_r}/build modules

Change-Id: Iea73e418065068f8451c42a2a3a4b46a9b5ffaac
Signed-off-by: Karol Lewandowski <k.lewandowsk@samsung.com>