aarch64: add SVE2 FP8DOT2 and FP8DOT4 intrinsics

aarch64: add SVE2 FP8DOT2 and FP8DOT4 intrinsics

This patch adds support for the following intrinsics:
- svdot[_f32_mf8]_fpm
- svdot_lane[_f32_mf8]_fpm
- svdot[_f16_mf8]_fpm
- svdot_lane[_f16_mf8]_fpm

The first two are available under a combination of the FP8DOT4 and SVE2 features.
Alternatively under the SSVE_FP8DOT4 feature under streaming mode.
The final two are available under a combination of the FP8DOT2 and SVE2 features.
Alternatively under the SSVE_FP8DOT2 feature under streaming mode.

gcc/
	* config/aarch64/aarch64-option-extensions.def
	(fp8dot4, ssve-fp8dot4): Add new extensions.
	(fp8dot2, ssve-fp8dot2): Likewise.
	* config/aarch64/aarch64-sve-builtins-base.cc (svdot_impl): Support fp8.
	(svdotprod_lane_impl): Likewise.
	(svdot_lane): Provide an unspec for fp8 types.
	* config/aarch64/aarch64-sve-builtins-shapes.cc
	(ternary_mfloat8_def): Add new class.
	(ternary_mfloat8): Add new shape.
	(ternary_mfloat8_lane_group_selection_def): Add new class.
	(ternary_mfloat8_lane_group_selection): Add new shape.
	* config/aarch64/aarch64-sve-builtins-shapes.h
	(ternary_mfloat8, ternary_mfloat8_lane_group_selection): Declare.
	* config/aarch64/aarch64-sve-builtins-sve2.def
	(svdot, svdot_lane): Add new DEF_SVE_FUNCTION_GS_FPM, twice to deal
	with the combination of features providing support for 32 and 16 bit
	floating point.
	* config/aarch64/aarch64-sve2.md (@aarch64_sve_dot<mode>): Add new.
	(@aarch64_sve_dot_lane<mode>): Likewise.
	* config/aarch64/aarch64.h:
	(TARGET_FP8DOT4, TARGET_SSVE_FP8DOT4): Add new defines.
	(TARGET_FP8DOT2, TARGET_SSVE_FP8DOT2): Likewise.
	* config/aarch64/iterators.md
	(UNSPEC_DOT_FP8, UNSPEC_DOT_LANE_FP8): Add new unspecs.
	* doc/invoke.texi: Document fp8dot4, fp8dot2, ssve-fp8dot4, ssve-fp8dot2
	extensions.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general-c/ternary_mfloat8_1.c: Add new.
	gcc.target/aarch64/sve/acle/general-c/ternary_mfloat8_lane_group_selection_1.c:
	Likewise.
	* gcc.target/aarch64/sve2/acle/asm/dot_lane_mf8.c: Likewise.
	* gcc.target/aarch64/sve2/acle/asm/dot_mf8.c: Likewise.
	* lib/target-supports.exp: Add dg-require-effective-target support for
	aarch64_asm_fp8dot2_ok, aarch64_asm_fp8dot4_ok,
	aarch64_asm_ssve-fp8dot2_ok and aarch64_asm_ssve-fp8dot4_ok.