* accelerate opencl compilation time test=develop

* fix style test=develop

* fix variant memory leak test=develop

* fix variant memory leak & fix style test=develop

* fix cpplint test=develop

* 1.add density_prior_box for gpu.
2.add flatten2 for gpu.
3.add concat 4 inputs size for gpu.
4.fix pool.
5.fix transpose2
test=develop

* 1.fix GetGPUTime
test=develop

* add opencl  depthwise_conv_trans_op

* test=develop

* refine toolchain test=develop

* fix wrap compilation error

* fix yolov3 armv8 compilation test=develop

* revert to armv7 as default test=develop

* fix fpga compilation test=develop

2.add flatten2 for gpu.
3.add concat 4 inputs size for gpu.
4.fix pool.
5.fix transpose2
test=develop

* [test=develop]1.fix crash when gpu op scale&elementwise_add input dim size equal 2
2.add gpu op mul

* fix code style test=develop

* Catch mobile exceptions test=develop

* code style format test=develop

* enable fast test compilation && push opencl kernels by run.py

* merge cl kernels into so

* restore pre-commit