riscv: Add a reset_cpu() function

The current do_reset() is called from a command context. Add a function
which can be used from anywhere, as is done on ARM. Adjust do_reset()
to call it.

Note that reset_cpu() is normally provided by SYSRESET so make this
declaration conditional on that being disabled.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Chanho Park <chanho61.park@samsung.com>
Tested-by: Chanho Park <chanho61.park@samsung.com>
diff --git a/arch/riscv/lib/reset.c b/arch/riscv/lib/reset.c
index 712e1bd..c4153c9 100644
--- a/arch/riscv/lib/reset.c
+++ b/arch/riscv/lib/reset.c
@@ -4,14 +4,11 @@
  */
 
 #include <command.h>
-#include <hang.h>
+#include <cpu_func.h>
 
 int do_reset(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 {
-	printf("resetting ...\n");
-
-	printf("reset not supported yet\n");
-	hang();
+	reset_cpu();
 
 	return 0;
 }