x86/fixmap: Modify fix_to_virt() to return a void pointer

x86/fixmap: Modify fix_to_virt() to return a void pointer

Almost all users of fix_to_virt() actually want a pointer.  Include the cast
within the definition, so the callers don't need to.

Two users which need the integer value are switched to using __fix_to_virt()
directly.  A few users stay fully unchanged, due to GCC's void pointer
arithmetic extension causing the same behaviour.  Most users however have
their explicit casting dropped.

Since __iomem is not used consistently in Xen, we drop it too.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>