accel/qaic: Add fifo size debugfs

accel/qaic: Add fifo size debugfs

Each DMA Bridge Channel (dbc) has a unique configured fifo size which is
specified by the userspace client of that dbc. Since the fifo is
circular, it is useful to know the configured size when debugging
issues.

Add a per-dbc subdirectory in debugfs and in each subdirectory add a
fifo_size entry that will display the size of that dbc's fifo 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/20240322175730.3855440-3-quic_jhugo@quicinc.com