Kbuild: Fix to pristine target.

This commit fixes the pristine target and removes
the complete set of hidden files:
 - .config.old
 - .version
 - .tinymountain.cmd
 - .tmp_versions

Change-Id: I6f96248885d504cb2a0f53849672c51b2d56e69a
Signed-off-by: Juan Manuel Cruz <juan.m.cruz.alcaraz@linux.intel.com>