main/openssl: change target for riscv64 to increase the performance
OpenSSL build for riscv64 should use linux64-riscv64
instead of linux-generic64
to leverage the functions written in RISC-V assembly.
The observed performance from the command openssl speed -evp aes-256-cbc
was increased around 11% - 14% on Milk-V Duo and 19% - 20% on VisionFive 2.