esp.c: introduce esp_update_drq() and update esp_fifo_{push, pop}_buf() to use it

esp.c: introduce esp_update_drq() and update esp_fifo_{push, pop}_buf() to use it

This new function sets the DRQ line correctly according to the current transfer
mode, direction and FIFO contents. Update esp_fifo_push_buf() and esp_fifo_pop_buf()
to use it so that DRQ is always set correctly when reading/writing multiple bytes
to/from the FIFO.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20240324191707.623175-15-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>