mtd: denali: remove nearly-duplicated register definitions

The controller has interrupt enable/status register pairs for each bank
(along with ECC and status registers) that differ only in address offset.
Rather than providing definitions for each register, make the address a
macro so that it scales for devices with different numbers of banks.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>