[fbgemm_gpu] Modularize CMake Code [WIP] #9882

Job	Run time
build-bazel (x86, linux.12xlarge, gcc)	9m 2s
build-bazel (x86, linux.12xlarge, clang)	8m 17s
build-linux (x86, linux.12xlarge, static, gcc)	17m 59s
build-linux (x86, linux.12xlarge, static, clang)	16m 50s
build-macos (macos-13, static)	19m 23s
build-linux (x86, linux.12xlarge, shared, gcc)	18m 10s
build-macos (macos-13, shared)	18m 32s
build-linux (x86, linux.12xlarge, shared, clang)	16m 36s
build-windows (windows-2022, static)	11m 43s
build-windows (windows-2022, shared)	12m 27s
	2h 28m 59s

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