mtd: cmdset_0002: add CFI 1.5 support for S29GL-S

This patch adds CFI 1.5 support for the new Spansion S29GL-S device family.
For details, see the data sheet on the Spansion web site:
http://www.spansion.com/Support/Datasheets/S29GL_128S_01GS_00_02_e.pdf

Signed-off-by: Gernot Hoyler <Gernot.Hoyler@spansion.com>
Acked-by: Guillaume LECERF <glecerf@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>