commit c627f2ce ("serial: 8250: Add support for big-endian MMIO accesses")
added support for 32-bit big-endian mmio to the 8250 driver. Support for
ioreadXXbe/iowriteXXbe io accessors was missing from m32r arch, which caused
build errors.

Add trivial macro mmio accessors.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Cc: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>