io-mapping: Fixup for different names of writecombine

io-mapping: Fixup for different names of writecombine

Somehow architectures can't agree on this. And for good measure make
sure we have a fallback which should work everywhere (fingers
crossed).

v2: Make it compile properly, needs a defined() for the #elif.

Fixes: ac96b5566926 ("io-mapping.h: s/PAGE_KERNEL_IO/PAGE_KERNEL/")
Cc: Chris Wilson <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: [email protected]
Reviewed-by: Chris Wilson <[email protected]>
Reviewed-by: Joonas Lahtinen <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]