accel/qaic: Add fifo queued debugfs

When debugging functional issues with workload input processing, it is
useful to know if requests are backing up in the fifo, or perhaps
getting stuck elsewhere. To answer the question of how many requests are
in the fifo, implement a "queued" debugfs entry per-dbc that returns the
number of pending requests when read.

Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Carl Vanderlip <quic_carlv@quicinc.com>
Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240322175730.3855440-4-quic_jhugo@quicinc.com