Enable arm64 neon scrypt implementation

It seems that old Scrypt-config.mk is unaware of arm64 architecture.
In fact, crypto_scrypt-neon.c can be compiled into arm64 as well.  This
CL adds an arch section for arm64.

Bug: 65425184
Test: adb shell /data/nativetest64/scrypt_test/scrypt_test
Change-Id: Ib451de642c7cc4548bfdc0879781981654b21b8f
Merged-In: If40a30378b8038324aad44071107130d7722e28d

crypto/scrypt/Scrypt-config.mk

@@ -82,7 +82,7 @@ target_src_files  := $(common_src_files) $($(target_arch)_src_files)
 target_src_files  := $(filter-out $($(target_arch)_exclude_files), $(target_src_files))
 
 # Hacks for ARM NEON support
-ifeq ($(target_arch),arm)
+ifneq (,$(filter $(target_arch), arm arm64))
 ifeq ($(ARCH_ARM_HAVE_NEON),true)
 target_c_flags   += $(arm_neon_c_flags)
 target_src_files += $(arm_neon_src_files)