riscv: Allow use of reset drivers

Currently, one cannot use a reset driver on RISC-V. Follow the MIPS
example, and disable the default reset handler when the sysreset driver is
enabled.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/riscv/lib/reset.c

@@ -7,6 +7,7 @@
 #include <command.h>
 #include <hang.h>
 
+#ifndef CONFIG_SYSRESET
 int do_reset(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 {
 	printf("resetting ...\n");
@@ -16,3 +17,4 @@ int do_reset(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 
 	return 0;
 }
+#endif