EDAC, skx: Move debugfs node under EDAC's hierarchy

The debugfs node is /sys/kernel/debug/skx_edac_test. Rename it and move
under EDAC debugfs root directory. Remove the unused 'skx_fake_addr' and
remove the 'skx_test' on error.

Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
CC: Mauro Carvalho Chehab <mchehab@kernel.org>
CC: arozansk@redhat.com
CC: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1542353684-13496-1-git-send-email-qiuxu.zhuo@intel.com