elf: Move elf_dynamic_do_Rel RTLD_BOOTSTRAP branches outside

elf_dynamic_do_Rel checks RTLD_BOOTSTRAP in several #ifdef branches.
Create an outside RTLD_BOOTSTRAP branch to simplify reasoning about the
function at the cost of a few duplicate lines.

Since dl_naudit is zero in RTLD_BOOTSTRAP code, the RTLD_BOOTSTRAP
branch can avoid _dl_audit_symbind calls to decrease code size.

Reviewed-by: Adheemrval Zanella <adhemerval.zanella@linaro.org>