mips: add <asm-generic/io.h> including

With the adding, some default ioremap_xx methods defined in
asm-generic/io.h can be used. E.g the default ioremap_uc() returning
NULL.

We also massaged various headers to avoid nested includes.

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
[jiaxun.yang@flygoat.com: Massage more headers, fix ioport defines]
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>