CVE-2021-47414 riscv: Flush current cpu icache before other cpus

In the Linux kernel, the following vulnerability has been resolved: riscv: Flush current cpu icache before other cpus On SiFive Unmatched, I recently fell onto the following BUG when booting: 0.000000 ftrace: allocating 36610 entries in 144 pages 0.000000 Oops - illegal instruction 1 0.000000...