aarch64: Make -mno-simd-memops default for aarch64*-*-elf targets

These targets are regularly used for embedded applications for
portions of code where the Advanced SIMD registers may not be
preserved, such as interrupt handlers.

Disabling the use of SIMD registers for memset/memcpy operations by
default ensures that code which doesn't overtly perform FPU or SIMD
operations won't end up using those registers unintentially.

Signed-off-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit d626b83)

Author: keith-packard

gcc/config/aarch64/aarch64-elf.h

@@ -144,4 +144,7 @@ ASM_MABI_SPEC
 #undef TYPE_OPERAND_FMT
 #define TYPE_OPERAND_FMT	"%%%s"
 
+#undef AARCH64_SIMD_MEMOPS_DEFAULT
+#define AARCH64_SIMD_MEMOPS_DEFAULT 0
+
 #endif /* GCC_AARCH64_ELF_H */