iomap: Use non-raw io functions for io{read|write}XXbe

Fix an asymmetry in the io{read|write}XXbe functions in that the
big-endian variants make use of the raw io accessors while the
little-endian variants use the regular accessors. Some architectures
implement barriers to order against both spinlocks and DMA accesses
and for these case, the big-endian variant of the API would not be
protected.

Thus, change the mmio_XXXXbe macros to use the appropriate swab() function
wrapping the regular accessor. This is similar to what was done for PIO.

When this code was originally written, barriers in the IO accessors were
not common and the accessors simply wrapped the raw functions in a
conversion to CPU endianness. Since then, barriers have been added in
some architectures and are now missing in the big endian variant of the
API.

This also manages to silence a few sparse warnings that check
for using the correct endian types which the original code did
not annotate correctly.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/CAK8P3a25zQDxyaY3iVv+JmSSzs7F6ssGc+HdBkGs54ZfViX+Fg@mail.gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>