Staging: hv: Eliminate driver_context structure

We need to move the following elements from struct driver_context:
class_id and driver in one step. As part of this operation get rid of
the struct driver_context. With this patch we will have
consolidated all driver state into one data structure:
struct hv_driver.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>