aux_serial: Increase UART DMA buffer sizes for USB HS

* usbd_ep_read_packet for a 64 byte FS bulk packet uses a 128-byte DMA bounce buffer okay,
  but for a 512 byte HS bulk packet will overflow it and corrupt adjacent .bss variables.
* Allocate more space for both buffers, fixing stlinkv3.

src/platforms/common/aux_serial.h

@@ -27,11 +27,14 @@
 
 #if defined(STM32F0) || defined(STM32F1) || defined(STM32F3) || defined(STM32F4) || defined(STM32F7)
 /* XXX: Does the st_usbfs_v2_usb_driver work on F3 with 128 byte buffers? */
-#if defined(STM32F1) || defined(STM32F3) || defined(STM32F4) || defined(STM32F7)
+#if defined(STM32F1) || defined(STM32F3) || defined(STM32F4)
 #define USART_DMA_BUF_SHIFT 7U
 #elif defined(STM32F0)
 /* The st_usbfs_v2_usb_driver only works with up to 64-byte buffers on the F0 parts */
 #define USART_DMA_BUF_SHIFT 6U
+#elif defined(STM32F7)
+/* HS bulk packets are 512 bytes, use 2x that */
+#define USART_DMA_BUF_SHIFT 10U
 #endif
 
 #define USART_DMA_BUF_SIZE   (1U << USART_DMA_BUF_SHIFT)