wasi-nn: Support multiple TFLite models (#2002)

Remove restrictions:
- Only 1 WASM app at a time
- Only 1 model at a time
   - `graph` and `graph-execution-context` are ignored

Refer to previous document:
e8d718096d/core/iwasm/libraries/wasi-nn/README.md

build-scripts/config_common.cmake

@@ -333,6 +333,11 @@ if (WAMR_BUILD_SGX_IPFS EQUAL 1)
 endif ()
 if (WAMR_BUILD_WASI_NN EQUAL 1)
   message ("     WASI-NN enabled")
+  add_definitions (-DWASM_ENABLE_WASI_NN=1)
+  if (WASI_NN_ENABLE_GPU EQUAL 1)
+      message ("     WASI-NN: GPU enabled")
+      add_definitions (-DWASI_NN_ENABLE_GPU=1)
+  endif ()
 endif ()
 if (WAMR_BUILD_ALLOC_WITH_USER_DATA EQUAL 1)
   add_definitions(-DWASM_MEM_ALLOC_WITH_USER_DATA=1)