Feature：Support flashMLA decoding via flashAttn2(#29)

Changes:
1. Implement flashMLA with matrix absorption algorithm via flashAttn2
2. Add golden test on MXMACA platform

README_MX.md

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+# FlashMLA on MXMACA
+We provide the implementation of FlashMLA from FlashAttention-2(version 2.6.3), based on MACA toolkit and C500 chips.
+
+FlashAttention-2 currently supports:
+1. Datatype fp16 and bf16.
+2. Multi-Token Parallelism = 1
+3. Paged kvcache with block size equal to 2^n (n >= 0)
+
+## How to run on MXMACA Device
+## Installation
+
+Requirements:
+- MXMACA GPUs.
+- MACA development toolkit.
+- Mctlass source code.
+- Pytorch2.0 from maca toolkit wheel package and above.
+
+To install flash attn in conda env:
+1. Make sure that maca pyTorch2.0 is installed.
+2. Download mctlass source code from: https://sw-download.metax-tech.com/
+
+### Set environment variables
+```bash
+export MACA_PATH=/your/maca/path
+export CUDA_PATH=$MACA_PATH/tools/cu-bridge
+export MACA_CLANG_PATH=$MACA_PATH/mxgpu_llvm/bin
+export LD_LIBRARY_PATH=$MACA_PATH/lib:$MACA_PATH/mxgpu_llvm/lib:$MACA_PATH/ompi/lib:$LD_LIBRARY_PATH
+```