RISC-V dummy kernel: move to dummy_kernel_bm
This MR moves the RISC-V bare metal dummy kernel from src/risc_v/dummy_kernel to src/risc_v/dummy_kernel_bm. This is done in preparation of !11149 (merged), in order to not further entangle the the bare metal and the Hermit dummy kernels, making it easier to eventually remove the former.
Edited by Victor Dumitrescu