um: Cleanup mem_32/64.c headers

Include only headers we really need.
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/mem_32.c

@@ -7,8 +7,7 @@
  */
 
 #include <linux/mm.h>
-#include <asm/page.h>
-#include <asm/mman.h>
+#include <asm/elf.h>
 
 static struct vm_area_struct gate_vma;
 

arch/x86/um/mem_64.c

 #include <linux/mm.h>
-#include <asm/page.h>
-#include <asm/mman.h>
+#include <asm/elf.h>
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {