[RUNTIME] Add fp16/fp32 conversion functions (#1766)

.gitmodules

3rdparty/HalideIR

3rdparty/compiler-rt/builtin_fp16.h

3rdparty/dlpack

3rdparty/dmlc-core

CMakeLists.txt

Makefile

apps/android_deploy/app/src/main/jni/Android.mk

apps/android_rpc/app/src/main/jni/Android.mk

apps/extension/Makefile

apps/howto_deploy/Makefile

apps/howto_deploy/tvm_runtime_pack.cc

apps/ios_rpc/tvmrpc.xcodeproj/project.pbxproj

apps/rocm_rpc/Makefile

apps/sgx/Makefile

nnvm/Makefile

nnvm/amalgamation/Makefile

python/setup.py

src/runtime/builtin_fp16.cc

tests/python/unittest/test_runtime_ndarray.py