s390x: snippets: c: Cleanup flat.lds

There are a lot of things in there which we don't need for snippets
and the alignments can be switched from 64K to 4K since that's the
s390 page size.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20230112154548.163021-3-frankja@linux.ibm.com
Message-Id: <20230112154548.163021-3-frankja@linux.ibm.com>