tests/qtest/boot-serial-test: Reorder pair of instructions in PL011 test

In the next commit we are going to use a different value
for the $w1 register, maintaining the same $x2 value. In
order to keep the next commit trivial to review, set $x2
before $w1.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/qtest/boot-serial-test.c

@@ -78,8 +78,8 @@ static const uint8_t bios_raspi2[] = {
 };
 
 static const uint8_t kernel_aarch64[] = {
-    0x81, 0x0a, 0x80, 0x52,                 /*        mov    w1, #'T' */
     0x02, 0x20, 0xa1, 0xd2,                 /*        mov    x2, #0x9000000  Load UART0 */
+    0x81, 0x0a, 0x80, 0x52,                 /*        mov    w1, #'T' */
     0x41, 0x00, 0x00, 0x39,                 /* loop:  strb   w1, [x2]        *TXDAT = 'T' */
     0xff, 0xff, 0xff, 0x17,                 /*        b      -4              (loop) */
 };