As per the current implementation of only single callback data gets
saved per event, driver is throwing an error if try to register multiple
callback for same event.

Add support of multiple callbacks data for same event. So agent can
register for same event with multiple callbacks. Here event management
driver will store the callbacks as list in Hash table entry for that event.

Here each callback data contain 2 element as callback handler and private
data of agent driver.
Signed-off-by: Abhyuday Godhasara <abhyuday.godhasara@xilinx.com>
Link: https://lore.kernel.org/r/20220427074803.19009-2-abhyuday.godhasara@xilinx.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>