hw/char/bcm2835_aux: Really use RX FIFO depth

While we model a 8-elements RX FIFO since the BCM2835 AUX model
was introduced in commit 97398d900ca ("bcm2835_aux: add emulation
of BCM2835 AUX block") we only read 1 char at a time!

Have the IOCanReadHandler handler return how many elements are
available, and use that in the IOReadHandler handler.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Luc Michel <luc.michel@amd.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250220092903.3726-6-philmd@linaro.org>

hw/char/bcm2835_aux.c

@@ -221,7 +221,7 @@ static int bcm2835_aux_can_receive(void *opaque)
 {
     BCM2835AuxState *s = opaque;
 
-    return s->read_count < BCM2835_AUX_RX_FIFO_LEN;
+    return BCM2835_AUX_RX_FIFO_LEN - s->read_count;
 }
 
 static void bcm2835_aux_put_fifo(void *opaque, uint8_t value)
@@ -243,7 +243,9 @@ static void bcm2835_aux_put_fifo(void *opaque, uint8_t value)
 
 static void bcm2835_aux_receive(void *opaque, const uint8_t *buf, int size)
 {
-    bcm2835_aux_put_fifo(opaque, *buf);
+    for (int i = 0; i < size; i++) {
+        bcm2835_aux_put_fifo(opaque, buf[i]);
+    }
 }
 
 static const MemoryRegionOps bcm2835_aux_ops = {