fifo8: introduce fifo8_peek() function

fifo8: introduce fifo8_peek() function

This allows uses to peek the byte at the current head of the FIFO.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240828122258.928947-9-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>