ggml: support CUDA's half type for aarch64(#1455)

support CUDA's half type for aarch64 in ggml_fp16_t definition

Author: KyL0N

ggml.h

@@ -255,9 +255,11 @@
 extern "C" {
 #endif
 
-#ifdef __ARM_NEON
+#if defined(__ARM_NEON) && !defined(GGML_CUDA_F16)
     // we use the built-in 16-bit float type
     typedef __fp16 ggml_fp16_t;
+#elif defined(GGML_CUDA_F16)
+    typedef half ggml_fp16_t;
 #else
     typedef uint16_t ggml_fp16_t;
 #endif