nvproxy: support NV_EVENT_BUFFER

Adds the NV_EVENT_BUFFER (0x90cd) event-record buffer API when `capProfiling` is enabled.

- Allocation classes: NV_EVENT_BUFFER (0x90cd), NV_EVENT_BUFFER_BIND (0x7f).
- Control commands: NV_EVENT_BUFFER_CTRL_CMD_{ENABLE_EVENTS,UPDATE_GET,FLUSH}, NV2080_CTRL_CMD_GR_FECS_BIND_EVTBUF_FOR_UID, NV2080_CTRL_CMD_EVENT_VIDEO_BIND_EVTBUF.

Validated with tools/nvidia_driver_differ and the driver struct parity test (20 supported drivers).