ipmi: make ipmi_class a static const structure

Now that the driver core allows for struct class to be in read-only
memory, move the ipmi_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: Corey Minyard <minyard@acm.org>
Cc: openipmi-developer@lists.sourceforge.net
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Message-Id: <20230620143701.577657-2-gregkh@linuxfoundation.org>
Signed-off-by: Corey Minyard <minyard@acm.org>