console: Support delete as well as backspace

Some terminals do not generate backspace correctly, so accept delete
as a substitute.

BUG=chrome-os-partner:10147
TEST=manual:
ssh into workstation, then telnet to serial port (with ser2net running)
See that the backspace key now works correctly, instead of injecting
strange characters into the terminal.

Change-Id: Ief6f2bcab9b8e82cb5720d18c596326b49ffc336
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/24715
Reviewed-by: Randall Spangler <rspangler@chromium.org>

common/uart_buffering.c

@@ -339,10 +339,10 @@ void uart_process(void)
 			 * don't interfere with the transmit buffer. */
 			if (c == '\n')
 				uart_write_char('\r');
-			uart_write_char(c);
+			uart_write_char(c == 0x7f ? '\b' : c);
 
 			/* Handle backspace if we can */
-			if (c == '\b') {
+			if (c == '\b' || c == 0x7f) {
 				handle_backspace();
 				continue;
 			}