fix: build from source with MPI & NCCL in other directories

[C1rN09]

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Motivation

Tried building lmdeploy from source with NCCL & MPI installed in other directory, here is my commands

mkdir build && cd build
NCCL_ROOT=/my/path/to/nccl bash ../generate.sh

This gets me wrong because

1. CMAKE_POLICY 0074 not enabled, so NCCL_ROOT doesn't work
2. MPI library path is hardcoded so mine was not found

Modification

1. Enable CMP0074
2. fix NCCL & MPI related paths

BC-breaking (Optional)

No

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
3. If the modification has a dependency on downstream projects of a newer version, this PR should be tested with all supported versions of downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.