s390/bitops: optimize set_bit() for constant values

Since zEC12 we have the interlocked-access facility 2 which allows to
use the instructions ni/oi/xi to update a single byte in storage with
compare-and-swap semantics.
So change set_bit(), clear_bit() and change_bit() to generate such code
instead of a compare-and-swap loop (or using the load-and-* instruction
family), if possible.
This reduces the text segment by yet another 8KB (defconfig).

Alternatively the long displacement variants niy/oiy/xiy could have
been used, but the extended displacement field is usually not needed
and therefore would only increase the size of the text segment again.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/head.S

@@ -437,7 +437,7 @@ ENTRY(startup_kdump)
 
 #if defined(CONFIG_64BIT)
 #if defined(CONFIG_MARCH_ZEC12)
-	.long 3, 0xc100efe3, 0xf46ce000, 0x00400000
+	.long 3, 0xc100efe3, 0xf46ce800, 0x00400000
 #elif defined(CONFIG_MARCH_Z196)
 	.long 2, 0xc100efe3, 0xf46c0000
 #elif defined(CONFIG_MARCH_Z10)