common/sfc_efx/base: complete EvQ creation on Riverhead

common/sfc_efx/base: complete EvQ creation on Riverhead

Client drivers relying on interrupts will fail to complete event
queue creation on Riverhead boards as the latter have no support
for INIT_DONE events which means that it's useless to wait until
initialisation callback is triggered by interrupt-driven polling.

Client drivers which avoid interrupt-driven polling still handle
INIT_DONE events by direct polling and will fail to do so.

Solve this problem by adding an extra poll-once method which
will be called by client drivers after queue creation (probably,
with driver-specific lock being held). The method will invoke
initialisation callback on Riverhead and do nothing on the other
boards. Then the drivers will proceed with normal waiting which
will complete immediately in the case of Riverhead.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>