gc_bba_test: add raw slot dumps to locate the response

Reading one byte and getting 0x00 cannot distinguish 'decode is wrong' from
'reply is late' -- a one-byte window has nowhere for a late answer to show up.
These two probes clock EIGHT data bytes and print every slot, so the position
of 0x17 (NWAYS) or 0x04 (device ID) gives the latency directly, the same way
bit-shift analysis turned 00 00 00 10 into 'correct, 22 bits late'.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

gc_bba_test/source/bba.c

@@ -4,6 +4,9 @@
 #include <ogc/lwp_watchdog.h>
 
 u32 bba_speed = EXI_SPEED32MHZ;   /* nominal name; ~27 MHz in reality */
+static int begin(void);
+static void end(void);
+
 u32 bba_gap_us = 16;              /* see bba.h -- 0 reproduces the raw failure */
 
 /* Busy-wait, not usleep(): we are holding the EXI lock with CS asserted, so
@@ -23,6 +26,9 @@ static void gap(void)
  *     write  [0xC0, addr>>8, addr&0xFF, 0x00] + N bytes
  * The trailing 0x00 is the device's prefetch window: the address completes a
  * whole byte before the data phase so the register file can fetch in time. */
+int begin_raw(void) { return begin(); }
+void end_raw(void) { end(); }
+
 static int begin(void)
 {
 	int tries;