mtd: onenand: add option and variable for cache program feature

mtd: onenand: add option and variable for cache program feature

A new option is added for cache program feature. A new variable
ongoing is introduced for onenand_chip to handle the multi-command
cache program operation.

Signed-off-by: Roman Tereshonkov <roman.tereshonkov@nokia.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>