ggml-hexagon: graceful fallback for older socs where rpcmem_alloc2 and FASTRPC_GET_UR...

ggml-hexagon: graceful fallback for older socs where rpcmem_alloc2 and FASTRPC_GET_URI is unsupported (#16987)

* support older socs where FASTRPC_GET_URI is unsupported

* added graceful fallback when FASTRPC_GET_URI call fails

* use weak symbols instead of loading libcdsprpc.so dynamically

* Add weak pragma for rpcmem_alloc2

* Remove weak declaration for rpcmem_alloc2 in ggml-hexagon.cpp

Removed weak declaration for rpcmem_alloc2.

* Enforce ndev to 1 for archs below v75

Force ndev to 1 for SoCs architectures lower than v75.