libusbhost: generates a static library

due to limitations of the droidboot OS used for POS,
there's a need for a static libusbhost library.

this permits to include libusbhost in droidboot

Change-Id: I0f0c07817ad19b773b466b69fd6e997877d41b34
Signed-off-by: Guillaume Ranquet <guillaumex.ranquet@intel.com>