net/sfc/base: implement vSwitch create/destroy

net/sfc/base: implement vSwitch create/destroy

The vSwitch create API takes an array of num_vports client driver
allocated vPort config entries where entry at index 0 contains the PF
configuration and rest num_vports-1 entries refer to vPort configuration
for VFs 0 to (num_vports-2). The required hierarchy
(vswitch/vport/vadaptor) is created within this API. The destroy API
tears down this hierarchy and releases memory for the vSwitch object.

Signed-off-by: Gautam Dawar <gdawar@solarflare.com>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>