mtd: m25p80: Add Spansion S25FL512S, S70FL01GS

S25FL512S = 64MiB single die, same family as S25FL256S
S70FL01GS = 2x S25FL512S dies in one package (separate chip selects)

These devices are not sampling yet, but they are expected to be very
similar to S25FL256S, which has been tested.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>