[MIPS] Make I/O helpers more customizable

[MIPS] Make I/O helpers more customizable

1. Move ioswab*() and __mem_ioswab*() to mangle-port.h.  This gets rid
   of CONFIG_SGI_IP22 from include/asm-mips/io.h.

2. Pass a virtual address to *ioswab*().  Then we can provide
   mach-specific *ioswab*() and can do every evil thing based on its
   argument.  It could be useful on machines which have regions with
   different endian conversion scheme.

3. Call __swizzle_addr*() _after_ adding mips_io_port_base.  This
   unifies the meaning of the argument of __swizzle_addr*() (always
   virtual address).  Then mach-specific __swizzle_addr*() can do every
   evil thing based on the argument.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>