mm/early_ioremap: declare early_memremap_pgprot_adjust()

The mm/ directory can almost fully be built with W=1, which would help
in local development.  One remaining issue is missing prototype for
early_memremap_pgprot_adjust().

Thus add a declaration for this function.  Use mm/internal.h instead of
asm/early_ioremap.h to avoid missing type definitions and unnecessary
exposure.

Link: https://lkml.kernel.org/r/20220314165724.16071-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/early_ioremap.c

@@ -17,6 +17,7 @@
 #include <linux/vmalloc.h>
 #include <asm/fixmap.h>
 #include <asm/early_ioremap.h>
+#include "internal.h"
 
 #ifdef CONFIG_MMU
 static int early_ioremap_debug __initdata;

mm/internal.h

@@ -154,6 +154,12 @@ extern unsigned long highest_memmap_pfn;
  */
 #define MAX_RECLAIM_RETRIES 16
 
+/*
+ * in mm/early_ioremap.c
+ */
+pgprot_t __init early_memremap_pgprot_adjust(resource_size_t phys_addr,
+					unsigned long size, pgprot_t prot);
+
 /*
  * in mm/vmscan.c:
  */