s390/boot: change initial program check handler to disabled wait psw

The program check handler of the kernel image points to
startup_pgm_check_handler. However an early program check which happens
while loading the kernel image will jump to potentially random code, since
the code of the program check handler is not yet loaded; leading to a
program check loop.

Therefore initialize it to a disabled wait psw and let the startup code set
the proper psw when everything is in memory.
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/boot/head.S

@@ -69,7 +69,7 @@ __HEAD
 	.org	__LC_EXT_NEW_PSW		# 0x1b0
 	.quad	0x0002000180000000,0x1b0	# disabled wait
 	.org	__LC_PGM_NEW_PSW		# 0x1d0
-	.quad	0x0000000180000000,startup_pgm_check_handler
+	.quad	0x0002000180000000,0x1d0	# disabled wait
 	.org	__LC_IO_NEW_PSW			# 0x1f0
 	.quad	0x0002000180000000,0x1f0	# disabled wait