s390/lib: export __delay

__delay is exported by most architectures, and may be used in modules.
Since it is not exported for s390, s390:allmodconfig currently fails
to build with

ERROR: "__delay" [drivers/net/phy/mdio-octeon.ko] undefined!

Fixes: a6d678645210 ("net: mdio-octeon: Modify driver to work on both
	ThunderX and Octeon")
Cc: Radha Mohan Chintakuntla <rchintakuntla@cavium.com>
Cc: David Daney <david.daney@cavium.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/lib/delay.c

@@ -26,6 +26,7 @@ void __delay(unsigned long loops)
          */
 	asm volatile("0: brct %0,0b" : : "d" ((loops/2) + 1));
 }
+EXPORT_SYMBOL(__delay);
 
 static void __udelay_disabled(unsigned long long usecs)
 {