Move requirements into their own directory (#12547)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/source/getting_started/installation/gpu/cuda.inc.md

@@ -148,7 +148,7 @@ To build vLLM using an existing PyTorch installation:
 git clone https://github.com/vllm-project/vllm.git
 cd vllm
 python use_existing_torch.py
-pip install -r requirements-build.txt
+pip install -r requirements/build.txt
 pip install -e . --no-build-isolation
 ```
 

docs/source/getting_started/installation/gpu/rocm.inc.md

@@ -84,7 +84,7 @@ Currently, there are no pre-built ROCm wheels.
     # Install dependencies
     $ pip install --upgrade numba scipy huggingface-hub[cli,hf_transfer] setuptools_scm
     $ pip install "numpy<2"
-    $ pip install -r requirements-rocm.txt
+    $ pip install -r requirements/rocm.txt
 
     # Build vLLM for MI210/MI250/MI300.
     $ export PYTORCH_ROCM_ARCH="gfx90a;gfx942"

docs/source/getting_started/installation/gpu/xpu.inc.md

@@ -25,7 +25,7 @@ Currently, there are no pre-built XPU wheels.
 ```console
 source /opt/intel/oneapi/setvars.sh
 pip install --upgrade pip
-pip install -v -r requirements-xpu.txt
+pip install -v -r requirements/xpu.txt
 ```
 
 - Finally, build and install vLLM XPU backend: