refactor(*): reduce Wsign-compare warning

[MLU] add some basic support for MLU, including related passes, kernels, gtests and some api in padddle_api.h
Passes：mlu_subgraph_pass ,mlu_postprocess_pass
Kernels:  act，batch_norm, concat, conv, elementwise, fc, interpolate, pool, scale, softmax

* [MLU] support resnet50 on MLU

* [MLU] support resnet50 on MLU

* fix conv 2-pad to 4-pad

* fix compute conv shape

* fix pad, test=develop

* change conv_depthwise_3x3s1_fp.cc name to conv3x3s1p01_depthwise_fp32.cc to distinguish between conv3x3s1_depthwise_fp32.cc

* delete printf note in conv3x3s1, test=develop

* delete printf note, test=develop

* delete gem_sdot.h, test=develop

it is coped from __gemm_sdot_meta_.h

* update compute padding, test=develop

* fix padding size, must be 2 or 4. test=develop

* fix format in operators/conv_op.cc, test=develop

* change #if 0 to #if 1, test=develop

* put 2-pad to 4-pad in AttachImpl, test=develop

* fix clang-format error inn tests/math/connv_compute_test, test=develop

* fix x86 test result error, test=develop

* add asymmetric padding test case in liite/tests/math/conv_compute.cc, test=develop

* change paddings type to support dynamically modify, test=develop

* fix x86 build error in connv_compute_test, test=develop

* fix opencl build error, test=develop

* fix oopencl build error, test=develop

* fix  opencl/conv_compute build error, test=develop

* fix  opencl/conv_compute build error, test=develop

* fix format in kernels/opencl/conv_computte_ttest,test=develop

* fix build error, test=develop

fix build error in kernels/x86/conv_compute.h

* Initial support for XPU
* Fix compiling errors of XPU
* Move XPU op kernel bridges from backends to kernels to fix deps order
* Change the namespace and directory of XPU bridges
* Add XPU SDK
* Fix header files and namespace of XPU SDK
* Add unit tests for relu and conv2d ops
* Restore the modification of paddle_api_test
* Supports simple model which contains only a relu layer
* Add compiling scripts for XPU
* Fix compiling errors of XPU
* Add comments for XPU LoadModel and BuildModel

* move lite/backends/npu/bridges --> lite/kernels/npu/

test=develop

* fix namespace for npu

test=develop

* mv npu runtime file to lite/backends/npu

test=develop

* [NPU] fix conv2d npu bridge, supports bias from input map
test=develop

* [NPU] support more dimensions for the bias of conv2d NPU bridge
test=develop