x86/boot: Fix memremap() related build failure

x86/boot: Fix memremap() related build failure

The following commit:

  5997efb96756 ("x86/boot: Use memremap() to map the MPF and MPC data")

causes new build failures on certain randconfigs:

  drivers/sfi/sfi_core.c: In function ‘sfi_map_memory’:
  drivers/sfi/sfi_core.c:104:10: error: implicit declaration of function ‘memremap’ [-Werror=implicit-function-declaration]
  drivers/sfi/sfi_core.c:104:31: error: ‘MEMREMAP_WB’ undeclared (first use in this function)

This is a case of parasitic header dependencies: the sfi_core.c file indirectly
includes <linux/io.h> for typical - but not all configs.

Including <linux/io.h> explicitly solves the build failure.

Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
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Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>