nor/flash: Add keep_alive() during flash write handler

Added keep_alive() call inside main flash write loop. Large
files where causing a gdb timeout warning.

Change-Id: I525dad2d644e248dd9ecf678e4d8e33c22eefdf2
Signed-off-by: Edward Fewell <efewell@ti.com>
Reviewed-on: http://openocd.zylin.com/5682
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/flash/nor/cc3220sf.c

@@ -363,6 +363,8 @@ static int cc3220sf_write(struct flash_bank *bank, const uint8_t *buffer,
 			LOG_ERROR("cc3220sf: Flash operation failed");
 			break;
 		}
+
+		keep_alive();
 	}
 
 	/* Do one word write for any final bytes less than a full word */