Always probing pmecc in the generic nand controller probe function and
bailing out if pmecc is missing, prevents the driver to be usable for
SoCs which do not have a pmecc hardware ecc engine like older sam9 SoCs,
for example at91sam9g20. Tested on sam9x60 that the call, which the
comment was moved to, is sufficient to probe the pmecc.
Signed-off-by: Alexander Dahl <ada@thorsis.com>