ARM: 7492/1: add strstr declaration for decompressors

With the generic unaligned.h, more kernel headers get pulled in including
dynamic_debug.h which needs strstr. As it is not really used, we only need
a declaration here.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/decompress.c

@@ -32,6 +32,9 @@ extern void error(char *);
 #  define Tracecv(c,x)
 #endif
 
+/* Not needed, but used in some headers pulled in by decompressors */
+extern char * strstr(const char * s1, const char *s2);
+
 #ifdef CONFIG_KERNEL_GZIP
 #include "../../../../lib/decompress_inflate.c"
 #endif