s390/vmlinux.lds.S: Prevent thunk functions from getting placed with normal text

s390/vmlinux.lds.S: Prevent thunk functions from getting placed with normal text

The s390 indirect thunks are placed in the .text.__s390_indirect_jump_*
sections.

Certain config options which enable -ffunction-sections have a custom
version of the TEXT_TEXT macro:

  .text.[0-9a-zA-Z_]*

That unintentionally matches the thunk sections, causing them to get
grouped with normal text rather than being handled by their intended
rule later in the script:

  *(.text.*_indirect_*)

Fix that by adding another period to the thunk section names, following
the kernel's general convention for distinguishing code-generated text
sections from compiler-generated ones.

Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>