uninline check_signature()

This is a rather bizarre thing to have inlined in io.h.  Stick it in lib/
instead.

While we're there, despaghetti it a bit, and fix its off-by-one behaviour when
passed a zero length.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/check_signature.c

@@ -0,0 +1,26 @@
+#include <linux/io.h>
+#include <linux/module.h>
+
+/**
+ *	check_signature		-	find BIOS signatures
+ *	@io_addr: mmio address to check
+ *	@signature:  signature block
+ *	@length: length of signature
+ *
+ *	Perform a signature comparison with the mmio address io_addr. This
+ *	address should have been obtained by ioremap.
+ *	Returns 1 on a match.
+ */
+
+int check_signature(const volatile void __iomem *io_addr,
+			const unsigned char *signature, int length)
+{
+	while (length--) {
+		if (readb(io_addr) != *signature)
+			return 0;
+		io_addr++;
+		signature++;
+	}
+	return 1;
+}
+EXPORT_SYMBOL(check_signature);