x86: Fix parse_reservetop() build failure on certain configs

Commit e67a807 ("x86: Fix 'reservetop=' functionality") added a
fixup_early_ioremap() call to parse_reservetop() and declared it
in io.h.

But asm/io.h was only included indirectly - and on some configs
not at all, causing a build failure on those configs.

Cc: Liang Li <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Wang Chen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Andrew Morton <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/mm/pgtable_32.c

@@ -18,6 +18,7 @@
 #include <asm/e820.h>
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
+#include <asm/io.h>
 
 unsigned int __VMALLOC_RESERVE = 128 << 20;