allow disabling DNOTIFY without EMBEDDED

Allow disabling DNOTIFY with CONFIG_EMBEDDED=n.

I'm currently running a kernel with dnotify disabled and I haven't run into
any problem.  Is there any popular application left that breaks without
dnotify support in the kernel?

Note that this patch does not remove dnotify support, it still defaults to
"y", and the help text recommends enabling it.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>