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. Ideally, Semihosting and LocalFilesystem should also be disabled on the other non-mbed LPC11UXX boards, but since they use the same target I was unable to determine how to accomplish this.