Fixed sleep and disabled semihosting on LPC11U35

I created 3 separate device.h headers for the three LPC11UXX targets,
and disabled the features that the LPC11U35 board doesn't have like
Semihosting and LocalFileSystem. I also made the call to
mbed_interface_disconnect() require DEVICE_SEMIHOSTING, which prevents
calls to sleep() from hanging the system on an LPC11U35.