m68k: io{read,write} accessors

[Brian Norris]

It appears that m68k doesn't properly define the io{read,write}
functions. I get complaints like this from my compile testing:

drivers/mtd/nand/nand_base.c: In function 'nand_write_buf':
drivers/mtd/nand/nand_base.c:216:2: error: implicit declaration of
function 'iowrite8_rep' [-Werror=implicit-function-declaration]
drivers/mtd/nand/nand_base.c: In function 'nand_read_buf':
drivers/mtd/nand/nand_base.c:231:2: error: implicit declaration of
function 'ioread8_rep' [-Werror=implicit-function-declaration]
drivers/mtd/nand/nand_base.c: In function 'nand_write_buf16':
drivers/mtd/nand/nand_base.c:247:2: error: implicit declaration of
function 'iowrite16_rep' [-Werror=implicit-function-declaration]
drivers/mtd/nand/nand_base.c: In function 'nand_read_buf16':
drivers/mtd/nand/nand_base.c:263:2: error: implicit declaration of
function 'ioread16_rep' [-Werror=implicit-function-declaration]

Brian