xyz-modem: Allow to cancel transfer also by CTRL+C

Currently it is possible to cancel loadx and loady commands by pressing
CTRL+X (CAN character) at least 3 times quickly.

All other U-Boot commands, including loadb and loads can be cancelled by
CTRL+C. So allow it also in xyz-modem code used by loadx and loady
commands. Implement it by handling CTRL+C (ETX character) in the same way
as CTRL+X (CAN character).

Due to how x/y-modem protocol works, it is required to press
CTRL+C or CTRL+X at least 3 times quickly.
Signed-off-by: NPali Rohár <pali@kernel.org>
Reviewed-by: NSimon Glass <sjg@chromium.org>

common/xyzModem.c

@@ -32,6 +32,7 @@
 /* Values magic to the protocol */
 #define SOH 0x01
 #define STX 0x02
+#define ETX 0x03		/* ^C for interrupt */
 #define EOT 0x04
 #define ACK 0x06
 #define BSP 0x08
@@ -283,6 +284,7 @@ xyzModem_get_hdr (void)
 	      hdr_found = true;
 	      break;
 	    case CAN:
+	    case ETX:
 	      xyz.total_CAN++;
 	      ZM_DEBUG (zm_dump (__LINE__));
 	      if (++can_total == xyzModem_CAN_COUNT)