mtd: m25p80: Rework probing/JEDEC code

Previosly the driver always tried JEDEC probing, assuming that non-JEDEC
chips will return '0'. But truly non-JEDEC chips (like CAT25) won't do
that, their behaviour on RDID command is undefined, so the driver should
not call jedec_probe() for these chips.

Also, be less strict on error conditions, don't fail to probe if JEDEC
found a chip that is different from what platform code told, instead
just print some warnings and use an information obtained via JEDEC. In
that case we should not trust partitions any longer, but they might be
still useful (i.e. they could protect some parts of the chip).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>