pds_core: add the aux client API

Add the client API operations for running adminq commands.
The core registers the client with the FW, then the client
has a context for requesting adminq services.  We expect
to add additional operations for other clients, including
requesting additional private adminqs and IRQs, but don't have
the need yet.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>