The {read,write}s{b,w,l} operations are not defined by all
architectures and are being removed from the asm-generic/io.h
interface.

This patch replaces the usage of these string functions in the mtd
gpio accessors with io{read,write}{8,16,32}_rep calls instead.
Signed-off-by: NMatthew Leach <matthew@mattleach.net>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>