wimax/i2400m: USB driver uses a configurable endpoint map

Newer generations of the i2400m USB WiMAX device use a different
endpoint map; in order to make it easy to support it, we make the
endpoint-to-function mapeable instead of static.

Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>