mtd: nand: add option to quieten off the no device found messgae

Add NAND_SCAN_SILENT_NODEV to chip->options to the user-worrying messages
'No NAND device found!!!'. This message often worries users (was three
exclamation marks really necessary?) and especially in systems such as the
Simtec Osiris where there may be optional NAND devices which are not
known until probe time.

Revised version of the original NAND_PROBE_SPECULATIVE patch after comments
by Artem Bityutskiy about adding a whole new call.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>