xtensa: bfd: fix TLS relocations generated for PIE

When generating TLS dynamic relocations the existing xtensa BFD code
treats linking to a PIE exactly as linking to a shared object, resulting
in generation of wrong relocations for TLS entries. Fix that and add
tests.

bfd/
	* elf32-xtensa.c (elf_xtensa_check_relocs): Use bfd_link_dll
	instead of bfd_link_pic. Add elf_xtensa_dynamic_symbol_p test
	when generating GOT entries.
	(elf_xtensa_relocate_section): Use bfd_link_dll instead of
	bfd_link_pic.
ld/
	* testsuite/ld-xtensa/tlspie.dd: New file.
	* testsuite/ld-xtensa/tlspie.rd: New file.
	* testsuite/ld-xtensa/tlspie.sd: New file.
	* testsuite/ld-xtensa/tlspie.td: New file.
	* testsuite/ld-xtensa/xtensa-linux.exp (TLS PIE transitions):
	New test.