hw/char/mcf_uart: Really use RX FIFO depth

While we model a 4-elements RX FIFO since the MCF UART model
was introduced in commit 20dcee94833 ("MCF5208 emulation"),
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>
Tested-by: Thomas Huth <huth@tuxfamily.org>
Reviewed-by: Thomas Huth <huth@tuxfamily.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250220092903.3726-9-philmd@linaro.org>

hw/char/mcf_uart.c

@@ -281,14 +281,16 @@ static int mcf_uart_can_receive(void *opaque)
 {
     mcf_uart_state *s = (mcf_uart_state *)opaque;
 
-    return s->rx_enabled && (s->sr & MCF_UART_FFULL) == 0;
+    return s->rx_enabled ? FIFO_DEPTH - s->fifo_len : 0;
 }
 
 static void mcf_uart_receive(void *opaque, const uint8_t *buf, int size)
 {
     mcf_uart_state *s = (mcf_uart_state *)opaque;
 
-    mcf_uart_push_byte(s, buf[0]);
+    for (int i = 0; i < size; i++) {
+        mcf_uart_push_byte(s, buf[i]);
+    }
 }
 
 static const MemoryRegionOps mcf_uart_ops = {