counter: Implement events_queue_size sysfs attribute

The events_queue_size sysfs attribute provides a way for users to
dynamically configure the Counter events queue size for the Counter
character device interface. The size is in number of struct
counter_event data structures. The number of elements will be rounded-up
to a power of 2 due to a requirement of the kfifo_alloc function called
during reallocation of the queue.

Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Link: https://lore.kernel.org/r/c914b2db2ea0a2637633bcc3e86ded3c94783f2e.1632884256.git.vilhelm.gray@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>