jffs2: Standardize JFFS_<LEVEL> uses

Use pr_<level> to prefix KBUILD_MODNAME via pr_fmt.

Remove obfuscating defines and use constants in pr_<level>
No need for a do {} while (0) for single statements.

Form of JFFS_<LEVEL> output changes from
"JFFS2 notice: " to "jffs2: notice: "

Added pr_fmt to xattr.c

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>