[AArch64] Improve immediate expansion [PR106583]

[AArch64] Improve immediate expansion [PR106583]

Improve immediate expansion of immediates which can be created from a
bitmask immediate and 2 MOVKs.  Simplify, refactor and improve efficiency
of bitmask checks.  Move various immediate handling functions together
to avoid forward declarations.

This reduces the number of 4-instruction immediates in SPECINT/FP by 10-15%.

gcc/

	PR target/106583
	* config/aarch64/aarch64.cc (aarch64_internal_mov_immediate)
	Add support for a bitmask immediate with 2 MOVKs.
	(aarch64_check_bitmask): New function after refactorization.
	(aarch64_bitmask_imm): Simplify replication of small modes.
	Split function into 64-bit only version for efficiency.
	(aarch64_move_imm): Move near other immediate functions.
	(aarch64_uimm12_shift): Likewise.
	(aarch64_clamp_to_uimm12_shift): Likewise.
	(aarch64_movk_shift): Likewise.
	(aarch64_replicate_bitmask_imm): Likewise.
	(aarch64_and_split_imm1): Likewise.
	(aarch64_and_split_imm2): Likewise.
	(aarch64_and_bitmask_imm): Likewise.
	(aarch64_movw_imm): Likewise.

gcc/testsuite/
	PR target/106583
	* gcc.target/aarch64/pr106583.c: Add new test.