csu: Implement and use _dl_early_allocate during static startup

This implements mmap fallback for a brk failure during TLS
allocation.

scripts/tls-elf-edit.py is updated to support the new patching method.
The script no longer requires that in the input object is of ET_DYN
type.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit f787e138)