mtd: nand_base: Use io{read, write}*_rep functions for transfer

This patch replaces the usage of loops in the nand_base code with
io{read,write}{8,16}_rep calls instead.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>