Before version 14.0.0 llvm's integrated assembler fails to handle some
displacement variants:

arch/s390/purgatory/head.S:108:10: error: invalid operand for instruction
 lg %r11,kernel_type-.base_crash(%r13)

Instead of working around this and given that this is already fixed
raise the minimum clang version from 13.0.0 to 14.0.0.
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://reviews.llvm.org/D113341
Link: https://lore.kernel.org/r/20220511120532.2228616-9-hca@linux.ibm.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>