sysutils: implement poweroff

kernel/arch/riscv64/src/sbi.rs

@@ -4,6 +4,8 @@ const EXT_HSM: u64 = 0x48534D;
 const EXT_TIME: u64 = 0x54494D45;
 const EXT_DBCN: u64 = 0x4442434E;
 const EXT_SPI: u64 = 0x735049;
+const EXT_SYSTEM_SHUTDOWN: u64 = 0x53525354;
+const EXT_SYSTEM_SHUTDOWN_LEGACY: u64 = 0x08;
 
 primitive_enum! {
     pub enum Status: i64 {
@@ -108,3 +110,9 @@ pub fn sbi_debug_console_write_byte(byte: u8) {
 pub fn sbi_set_timer(next_event: u64) {
     unsafe { sbi_do_call(EXT_TIME, 0x00, next_event, 0, 0, 0, 0, 0) }.ok();
 }
+
+pub fn sbi_system_shutdown() -> ! {
+    unsafe { sbi_do_call(EXT_SYSTEM_SHUTDOWN, 0x00, 0, 0, 0, 0, 0, 0) }.ok();
+    unsafe { sbi_do_call(EXT_SYSTEM_SHUTDOWN_LEGACY, 0x00, 0, 0, 0, 0, 0, 0) }.ok();
+    unreachable!()
+}