fifo8: add fifo8_peek_buf() function

fifo8: add fifo8_peek_buf() function

This is a wrapper function around fifo8_peekpop_buf() that allows the
caller to peek into the FIFO, including handling the case where there
is a wraparound of the internal FIFO buffer.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240828122258.928947-8-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>