AArch64: Improve GOT addressing

AArch64: Improve GOT addressing

Improve GOT addressing by treating the instructions as a pair.  This reduces
register pressure and improves code quality significantly.  SPECINT2017
improves by 0.6% with -fPIC and codesize is 0.73% smaller.  Perlbench has
0.9% smaller codesize, 1.5% fewer executed instructions and is 1.8% faster
on Neoverse N1.

ChangeLog:
2021-11-02  Wilco Dijkstra  <wdijkstr@arm.com>

	* config/aarch64/aarch64.md (movsi): Add alternative for GOT accesses.
	(movdi): Likewise.
	(ldr_got_small_<mode>): Remove pattern.
	(ldr_got_small_sidi): Likewise.
	* config/aarch64/aarch64.c (aarch64_load_symref_appropriately): Keep
	GOT accesses as moves.
	(aarch64_print_operand): Correctly print got_lo12 in L specifier.
	(aarch64_mov_operand_p): Make GOT accesses valid move operands.
	* config/aarch64/constraints.md: Add new constraint Usw for GOT access.