s390/mm: Remove have_store_indication static key

s390/mm: Remove have_store_indication static key

Whenever test_facility() is used with a constant facility
number the generated code is identical to a static branch.

Remove the extra initcall and static_branch_enable() handling for
have_store_indication, and use test_facility() directly.

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>