elf: Fix elf_get_dynamic_info() for bootstrap

THe d6d89608 broke powerpc for --enable-bind-now because it turned
out that different than patch assumption rtld elf_get_dynamic_info()
does require to handle RTLD_BOOTSTRAP to avoid DT_FLAGS and
DT_RUNPATH (more specially the GLRO usage which is not reallocate
yet).

This patch fixes by passing two arguments to elf_get_dynamic_info()
to inform that by rtld (bootstrap) or static pie initialization
(static_pie_bootstrap).  I think using explicit argument is way more
clear and burried C preprocessor, and compiler should remove the
dead code.

I checked on x86_64 and i686 with default options, --enable-bind-now,
and --enable-bind-now and --enable--static-pie.  I also check on
aarch64, armhf, powerpc64, and powerpc with default and
--enable-bind-now.