EDAC: Carve out debugfs functionality

... into a separate compilation unit and drop a couple of
CONFIG_EDAC_DEBUG ifdefferies. Rename edac_create_debug_nodes() to
edac_create_debugfs_nodes(), while at it.

No functionality change.

Cc: <linux-edac@vger.kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>