haven: doorbell: Pass cap_table_entry as irq private

The threaded interrupt handler needs access to the cap_table_entry
structure and the clients passed in private data. All this information
is store in the cap_table_entry struct. Pass this in as irq private
data instead of the clients private pointer.

Change-Id: If2455704236f3531724d5c007210559391e5cfd8
Signed-off-by: Chris Lew <clew@codeaurora.org>