[Morello] TLS Descriptor support

[Morello] TLS Descriptor support

This change adds basic support for TLS descriptors.  Relaxation of
TLSDESC_GD to other relocations is limited to TLS_LE, other cases end
up retaining TLSDESC_GD.

There is one key difference from A64 for TLSDESC_GD -> LE transition
and that is in the case of static non-pie binaries.  Morello
TLSDESC_GD relocations are relaxed to LE for static non-pie binaries
since it ought to be safe to do so and it aligns with llvm behaviour.

bfd/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* elfnn-aarch64.c (IS_AARCH64_TLSDESC_RELOC): Add Morello
	relocations.
	(elfNN_aarch64_tlsdesc_small_plt_c64_entry): New Morello
	tlsdesc PLT entry.
	(elfNN_aarch64_howto_table): Add TLSDESC_ADR_PAGE20,
	TLSDESC_LD128_LO12, TLSDESC_CALL, TLSDESC relocations for
	Morello.
	(aarch64_tls_transition_without_check): Add INFO and
	MORELLO_RELOC arguments.  Add morello TLSDESC relocations.
	(aarch64_reloc_got_type, elfNN_aarch64_final_link_relocate,
	elfNN_aarch64_tls_relax, elfNN_aarch64_check_relocs,
	aarch64_can_relax_tls): Add morello TLSDESC relocations.
	(aarch64_tls_transition): Add transitions for morello TLSDESC
	relocations.
	(elfNN_aarch64_tls_relax): Add relaxations for morello
	TLSDESC.
	(elfNN_aarch64_relocate_section): Emit dynamic relocation for
	Morello static relocations.
	(elfNN_aarch64_allocate_dynrelocs): Allocate dynamic
	relocation space for Morello TLSDESC.
	(elfNN_aarch64_finish_dynamic_sections): Emit Morello tlsdesc
	PLT entry.
	* elfxx-aarch64.c (_bfd_aarch64_elf_put_addend,
	_bfd_aarch64_elf_resolve_relocation): Add Morello relocations.
	* reloc.c: Add Morello relocations.
	* bfd-in2.h: Regenerate.
	* libbfd.h: Regenerate.

gas/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* config/tc-aarch64.c (s_tlsdesccall): Emit Morello
	TLSDESC_CALL in C64 code.
	(reloc_table): Add Morello relocation.
	(md_apply_fix): Emit Morello TLSDESC_LD128_LO12 in C64 code.
	(aarch64_force_relocation): Add Morello TLSDESC relocations.
	* testsuite/gas/aarch64/morello-tlsdesc-c64.d: New file.
	* testsuite/gas/aarch64/morello-tlsdesc.d: New file.
	* testsuite/gas/aarch64/morello-tlsdesc.s: New file.

include/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* elf/aarch64.h: New Morello TLSDESC relocations.

ld/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* testsuite/ld-aarch64/morello-tlsdesc.s: New file.
	* testsuite/ld-aarch64/morello-tlsdesc.d: New test.
	* testsuite/ld-aarch64/morello-tlsdesc-static.d: New test.
	* testsuite/ld-aarch64/morello-tlsdesc-staticpie.d: New test.
	* testsuite/ld-aarch64/aarch64-elf.exp: Add them.