powerpc: boot: add strrchr function

libfdt gained a new dependency on strrchr, so copy the implementation
from lib/string.c. Most of the string functions are in assembly, but
stdio.c already has strnlen, so add strrchr there.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Rob Herring <robh@kernel.org>

arch/powerpc/boot/stdio.c

@@ -21,6 +21,16 @@ size_t strnlen(const char * s, size_t count)
 	return sc - s;
 }
 
+char *strrchr(const char *s, int c)
+{
+	const char *last = NULL;
+	do {
+		if (*s == (char)c)
+			last = s;
+	} while (*s++);
+	return (char *)last;
+}
+
 #ifdef __powerpc64__
 
 # define do_div(n, base) ({						\

arch/powerpc/boot/string.h

@@ -7,6 +7,7 @@ extern char *strcpy(char *dest, const char *src);
 extern char *strncpy(char *dest, const char *src, size_t n);
 extern char *strcat(char *dest, const char *src);
 extern char *strchr(const char *s, int c);
+extern char *strrchr(const char *s, int c);
 extern int strcmp(const char *s1, const char *s2);
 extern int strncmp(const char *s1, const char *s2, size_t n);
 extern size_t strlen(const char *s);