mtd: nand_ids: use size macros

Use the convenient 'SZ_8K' and 'SZ_16K' macros for the eraseblock size in the
NAND IDs table. This is a little more readable.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>