Don't adjust LOAD segment to match GNU_RELRO segment

Instead, fix Jakub's original code setting up the PR_GNU_RELRO header
from the PT_LOAD header.

	PR ld/14207
	PR ld/16322
	PR binutils/16323
bfd/
	* elf.c (assign_file_positions_for_load_sections): Revert last change.
	(assign_file_positions_for_non_load_sections): When setting up
	PT_GNU_RELRO header, don't require a corresponding PT_LOAD
	header that completely covers the relro region.
ld/
	* ldlang.c (lang_size_sections): Remove unneeded RELRO base
	adjust.  Tidy comments.
	* ld.texinfo (DATA_SEGMENT_RELRO_END): Correct description.
ld/testsuite/
	* ld-x86-64/pr14207.d: Adjust