adds CPU_ARCH to riscv_common preparing to handle it like cortex-m does adds CPU_CORE to gd32v
This adds support for the gd32v class devices from Gigadevice. The gd32vf103 contains an 108 MHz RISC-V core with similar peripherals as the stm32f1 devices Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
