target: fix messages and return values of failed op because not halted

Lot of messages was logged as LOG_WARNING, but the operation failed
immediately. Sometimes no error message was logged at all.
Add missing messages, change warnings to errors.

Sometimes ERROR_TARGET_INVALID was returned. Some command handlers
returned ERROR_OK! Always return ERROR_TARGET_NOT_HALTED.

While on it use LOG_TARGET_ERROR() whenever possible.
Prefix command_print() message with 'Error:' to get closer
to LOG_TARGET_ERROR() variant.

Error message was not added to get() and set() methods of
struct xxx_reg_type - the return value is properly checked and a message
is logged by the caller in case of ERROR_TARGET_NOT_HALTED.

Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Change-Id: I2fe4187c6025f0038956ab387edbf3f461c69398
Reviewed-on: https://review.openocd.org/c/openocd/+/7819
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/riscv/riscv.c

@@ -1840,7 +1840,7 @@ static int riscv_run_algorithm(struct target *target, int num_mem_params,
 	}
 
 	if (target->state != TARGET_HALTED) {
-		LOG_WARNING("target not halted");
+		LOG_TARGET_ERROR(target, "not halted (run target algo)");
 		return ERROR_TARGET_NOT_HALTED;
 	}