staging: axis-fifo: convert to use miscdevice

Using a struct class, a cdev, and another device just for a single minor
device is total overkill.  Just use a dynamic misc device instead,
saving lots of logic and memory.

Cc: Jacob Feder <jacobsfeder@gmail.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Muhammad Usama Anjum <musamaanjum@gmail.com>
Link: https://lore.kernel.org/r/YTdPvBgKW6cKYrvb@kroah.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>