Store the offset of the KDOORBELL and GTS registers in the softc.

[jhb]

Summary

Store the offset of the KDOORBELL and GTS registers in the softc.

VF devices use a different register layout than PF devices. Storing
the offset in a value in the softc allows code to be shared between the
PF and VF drivers.

Test Plan

• compiled and booted a kernel and verified ping still works

[np]

All egress queues including freelists use the BAR2 doorbell (aka UDB) and not the KDOORBELL by default. You might have to manually remove the setbit(&sc->doorbells, DOORBELL_UDB) in map_bar_2 to test this change for egress queues. See sysctl dev.t5nex.0.doorbells for the doorbells available to the driver.