s390/sclp: avoid potential usage of uninitialized value

sclp_early_printk could be used before .bss section is zeroed
(i.e. from als.c during the decompressor phase), therefore values used
by sclp_early_printk should be located in the .data section.

Another reason for that is to avoid potential initrd corruption, if some
code in future would use sclp_early_printk before initrd is moved from
possibly overlapping with .bss section region to a safe location.

Fixes: 0b0d1173

 ("s390/sclp: 32 bit event mask compatibility mode")
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>