net: ipa: assign endpoint to a resource group

The IPA hardware manages various resources (e.g. descriptors)
internally to perform its functions.  The resources are grouped,
allowing different endpoints to use separate resource pools.  This
way one group of endpoints can be configured to operate unaffected
by the resource use of endpoints in a different group.

Endpoints should be assigned to a resource group, but we currently
don't do that.

Define a new resource_group field in the endpoint configuration
data, and use it to assign the proper resource group to use for
each AP endpoint.

Tested-by: Sujit Kautkar <sujitka@chromium.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>