serial: 将 CMD_FLASH_END 作为单独的 soft reset 提供

该问题由 03e057b 引入，会导致每烧完一个分区后
芯片被软复位。

该问题的影响：

* 在 CSK4 中，该问题会导致第2个及之后的分区烧录失败，或带上 --verify-all 烧录
  没有响应
* 在 CSK6 中，会导致烧录第1个分区之后退回 ROM code loader (若 PB1 仍下拉)，由
  ROM code 完成余下分区的烧录

cskburn/src/main.c

@@ -674,13 +674,15 @@ serial_burn(uint32_t *addrs, char **images, int parts)
 		}
 	}
 
+	cskburn_serial_soft_reset(dev);
+
 	LOGI("Finished");
 	ret = true;
 
 err_write:
 	free(image_buf);
 err_enter:
-	cskburn_serial_reset(dev, options.reset_delay);
+	cskburn_serial_hard_reset(dev, options.reset_delay);
 	cskburn_serial_close(&dev);
 err_open:
 	return ret;

libcskburn_serial/include/cskburn_serial.h

@@ -28,6 +28,8 @@ bool cskburn_serial_verify(
 
 bool cskburn_serial_read_chip_id(cskburn_serial_device_t *dev, uint64_t *chip_id);
 
-bool cskburn_serial_reset(cskburn_serial_device_t *dev, uint32_t reset_delay);
+bool cskburn_serial_soft_reset(cskburn_serial_device_t *dev);
+
+bool cskburn_serial_hard_reset(cskburn_serial_device_t *dev, uint32_t reset_delay);
 
 #endif  // __LIB_CSKBURN_SERIAL__

libcskburn_serial/src/core.c

@@ -293,8 +293,6 @@ cskburn_serial_write(cskburn_serial_device_t *dev, uint32_t addr, uint8_t *image
 	}
 #endif  // FEATURE_MD5_CHALLENGE
 
-	cmd_flash_finish(dev);
-
 	uint64_t t2 = time_monotonic();
 
 	uint32_t spent = (uint32_t)((t2 - t1) / 1000);
@@ -330,7 +328,13 @@ cskburn_serial_read_chip_id(cskburn_serial_device_t *dev, uint64_t *chip_id)
 }
 
 bool
-cskburn_serial_reset(cskburn_serial_device_t *dev, uint32_t reset_delay)
+cskburn_serial_soft_reset(cskburn_serial_device_t *dev)
+{
+	return cmd_flash_finish(dev);
+}
+
+bool
+cskburn_serial_hard_reset(cskburn_serial_device_t *dev, uint32_t reset_delay)
 {
 	serial_set_rts(dev->handle, !rts_active);  // UPDATE=HIGH
 	serial_set_dtr(dev->handle, SERIAL_LOW);  // RESET=LOW