TLSR951x also supports Andes extended CSR. Reworks the following CSR handling to use the RISC-V custom CSR common code: 1. Use common macros for HWDSP CSR context save/restore. 2. Use common macros for PFT CSR context save/restore. 3. Use common low-level CSR initialization via __reset hook. Signed-off-by: Jimmy Zheng <jimmyzhe@andestech.com>