x86: update AS_* macros to binutils >=2.23, supporting ADX and AVX2

Now that the kernel specifies binutils 2.23 as the minimum version, we
can remove ifdefs for AVX2 and ADX throughout.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

lib/raid6/test/Makefile

@@ -35,9 +35,6 @@ endif
 ifeq ($(IS_X86),yes)
         OBJS   += mmx.o sse1.o sse2.o avx2.o recov_ssse3.o recov_avx2.o avx512.o recov_avx512.o
         CFLAGS += -DCONFIG_X86
-        CFLAGS += $(shell echo "vpbroadcastb %xmm0, %ymm1" |	\
-                    gcc -c -x assembler - >/dev/null 2>&1 &&	\
-                    rm ./-.o && echo -DCONFIG_AS_AVX2=1)
 	CFLAGS += $(shell echo "vpmovm2b %k1, %zmm5" |          \
 		    gcc -c -x assembler - >/dev/null 2>&1 &&	\
 		    rm ./-.o && echo -DCONFIG_AS_AVX512=1)