MIPS: sync I/O related header files with linux-4.4

Mainly sync asm/io.h to get a working ioremap() implementation
as well as the full set of I/O accessors. Pull in additional
header files to make this work.

Furthermore port over the directory 'arch/mips/include/asm/mach-generic/'
with contains default definitions for I/O and memory spaces and default
implementations for mapping those spaces. All files in that directory
can be overwritten by a SoC/machine.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>