arm64: crypto: use CC_FLAGS_FPU for NEON CFLAGS

Now that CC_FLAGS_FPU is exported and can be used anywhere in the source
tree, use it instead of duplicating the flags here.

Link: https://lkml.kernel.org/r/20240329072441.591471-6-samuel.holland@sifive.com
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian König <christian.koenig@amd.com> 
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: WANG Xuerui <git@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: SiFiveHolland

arch/arm64/lib/Makefile

@@ -7,10 +7,8 @@ lib-y		:= clear_user.o delay.o copy_from_user.o		\
 
 ifeq ($(CONFIG_KERNEL_MODE_NEON), y)
 obj-$(CONFIG_XOR_BLOCKS)	+= xor-neon.o
-CFLAGS_REMOVE_xor-neon.o	+= -mgeneral-regs-only
-CFLAGS_xor-neon.o		+= -ffreestanding
-# Enable <arm_neon.h>
-CFLAGS_xor-neon.o		+= -isystem $(shell $(CC) -print-file-name=include)
+CFLAGS_xor-neon.o		+= $(CC_FLAGS_FPU)
+CFLAGS_REMOVE_xor-neon.o	+= $(CC_FLAGS_NO_FPU)
 endif
 
 lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o