fix cv v8 build error, test=develop

test=develop

* [LITE][OPENCL] enhance elemul, fix reshape for opencl. test=develop

* comment loop test for pad2 opencl kernel. test=develop

* [LITE][PROFILE] add sequnce statics for precision profiler. test=develop

* rename elementwise_sub_grad, test=develop

* rename Grad to GRAD, test=develop

* deal with case that Y@GRAD is empty, test=develop

* fix ci for test_mobilenetv1/v2. test=develop

* [OPENCL][CI] add test_mobilenetv1/v2 for opencl ci. test=develop

* [LITE][OPENCL][Image]optimise conv2d 5x5 7x7,test=develop

* [LITE][OPENCL][Image]optimise conv2d 5x5 7x7,test=develop

* [LITE][OPENCL][Image]optimise conv2d 5x5 7x7,test=develop

* [LITE][OPENCL] comment vlog for opencl kernel. test=develop

* fxi ff, test=develop

* delete bgr_flip, test=develop

* Ehance mobilenetv1/v2, add std_dev computation. test=develop

* Ehance cxx mobile_light demo, add std_dev computation. test=develop

* rm grad code

* [LITE][OPENCL] clean code for opencl. test=develop

* [LITE][PROFILER] Enhance Precision Profiler. test=develop

* delete useless var in profiler. test=develop

* add ocl header. test=develop

* rm grad code

* add mul_grad, test=develop

* add strip lib in ios

* add strip lib in ios test=develop

* fix memory leaky, test=develop

* [LITE][OPENCL] Change fp32 fc to fp16's. test=develop

* fix act in conv3x3opt opencl kernel. test=develop

* [LITE][CMAKE] fix cmake for opencl tiny_pubish compile. test=develop

* Fix OpenCL kernel of exp, tanh,

* Fix layout pass for opencl backend,

* Add how to debug cl kernel. test=develop.

This reverts commit 670fcc3c.

add cuda c++ doc