mtd/cfi_flash: fix write problems for Numonyx P33/30 32 MBit flashs

commit 54652991
Work around bug in Numonyx P33/P30 256-Mbit 65nm flash chips

fixes a problem for Numonyx P33/P30 flashes for 256-Mbit, but this leads
to problems for smaller versions of this chip e.g. the 32Mbit version
with deviceid 0x16 on mgcoge. So move the code for this work around to
an own function and check previously manufacturer id and device id to
not break other flashes which don't need this work around.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
cc: Stefan Roese <sr@denx.de>
cc: Philippe De Muyter <phdm@macqel.be>
cc: Gerlando Falauto <gerlando.falauto@keymile.com>
Signed-off-by: Stefan Roese <sr@denx.de>