jffs2: Convert most D1/D2 macros to jffs2_dbg

D1 and D2 macros are mostly uses to emit debugging messages.

Convert the logging uses of D1 & D2 to jffs2_dbg(level, fmt, ...)
to be a bit more consistent style with the rest of the kernel.

All jffs2_dbg output is now at KERN_DEBUG where some of
the previous uses were emitted at various KERN_<LEVEL>s.

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>