alpha: Use generic <asm-generic/io.h>

This enables the alpha to use <asm-generic/io.h> to fill in the
missing (undefined) I/O accessor functions.

This is needed if Alpha ever wants to uses CONFIG_REGMAP_MMIO
which has been patches to use accelerated _noinc accessors
such as readsq/writesq that Alpha, while being a 64bit platform,
as of now not yet provide. readq/writeq is however provided
so the machine can do 64bit I/O.

This comes with the requirement that everything the architecture
already provides needs to be defined, rather than just being,
say, static inline functions.

Bite the bullet and just provide the definitions and make it work.

Some defines need to be piled right before the inclusion of
<asm-generic/io.h> due to the fact that alpha is including
<asm-generic/iomap.h> without selecting GENERIC_IOMAP.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-alpha@vger.kernel.org
Link: https://lore.kernel.org/linux-mm/202208181447.G9FLcMkI-lkp@intel.com/


Signed-off-by: Arnd Bergmann <arnd@arndb.de>