USB: xhci: Refactor input device context setup.

Refactor common code to set up the add and drop flags for the input device
context setup.  This setup is used before a configure endpoint command for
the reset endpoint quirk, and will be used for the command to alloc or
free streams rings.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>