QEMU SIFIVE reading from stdin hangs
Description of problem:
I have a simple test program (C and ASM) that reads from stdin.  When i was using the qemu provided by Ubuntu, QEMU emulator version 8.0.4 (Debian 1:8.0.4+dfsg-1ubuntu3.23.10.5), my test was working, and was able to read bytes from stdin.

Using the latest Qemu from git, breaks my test.  I can still print, but now reading hangs, like its always waiting for input but never getting it.

My guess is that this commit breaks my code:
https://github.com/qemu/qemu/commit/6ee7ba1b8a10bd8eb1d3b918eaaf9f832a51adb4

Before the above commit, `qemu_chr_fe_set_handlers` was being called, and that is what allowed the default behavior of reading from stdin is on by default?

from sifive_uart.c
```
    qemu_chr_fe_set_handlers(&s->chr, sifive_uart_can_rx, sifive_uart_rx,
                             sifive_uart_event, sifive_uart_be_change, s,
                             NULL, true);
```
Steps to reproduce:
1. compile simple C program that calls `read` reading a single byte from stdin
2. do not initialize UART options
3. run in QEMU, send input, hangs.
Additional information:
Other examples online, like riscv-probe, use a uart init function like below:
```
static void sifive_uart_init()
{
    uart = (int *)(void *)getauxval(SIFIVE_UART0_CTRL_ADDR);
    uint32_t uart_freq = getauxval(UART0_CLOCK_FREQ);
    uint32_t baud_rate = getauxval(UART0_BAUD_RATE);
    uint32_t divisor = uart_freq / baud_rate - 1;
    uart[UART_REG_DIV] = divisor;
    uart[UART_REG_TXCTRL] = UART_TXEN;
    uart[UART_REG_RXCTRL] = UART_RXEN;
    uart[UART_REG_IE] = 0;
}
```

However, when I was using QEMU 8.0.4, i did not have to write a function like above to init UART, because stdin and stdout were working out of the box.
Below is my C and ASM: