target: riscv: move the SMP commands under riscv

For all the targets that support SMP, the sub-commands 'smp' and
'smp_gdb' are under the arch name:
- aarch64 smp
- cortex_a smp
- cortex_m smp
- esp32 smp
- mips_m4k smp

Keep consistency among OpenOCD commands, and move under the arch
name 'riscv' the SMP subcommands.

Change-Id: Iede7841c2df8161ff2c6fea3be561d1f26ad6cd0
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/9165
Reviewed-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins

src/target/riscv/riscv.c

@@ -5838,6 +5838,9 @@ static const struct command_registration riscv_exec_command_handlers[] = {
 			"When off, users need to take care of memory coherency themselves, for example by using "
 			"`riscv exec_progbuf` to execute fence or CMO instructions."
 	},
+	{
+		.chain = smp_command_handlers
+	},
 	COMMAND_REGISTRATION_DONE
 };
 
@@ -5870,9 +5873,6 @@ static const struct command_registration riscv_command_handlers[] = {
 		.usage = "",
 		.chain = semihosting_common_handlers
 	},
-	{
-		.chain = smp_command_handlers
-	},
 	COMMAND_REGISTRATION_DONE
 };