s390/sclp: clean up unneeded .data section usage

Since commit 980d5f9a ("s390/boot: enable .bss section for compressed
kernel") .bss section usage is no longer restricted. .bss section is a
part of the decompressor's image and is zeroed by the linker. For that
reason clean up now unneeded .data section usage.

Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>