Patch some serious errors in im2sb and intelmote2 DMA & SPI code

- first bits of LIS3L02Q acceleration values are no longer cut off, allowing sign recovery
- early setting of descriptorless mode for DMA controller (as needed for it to function)
- correction of I2C address of TMP175 on im2 sensor board (is 0x4a as stated in imote2 datasheet)
- using atomic variable access
- making HalPXA27xSSPControlP generic, as multiple SPI interfaces might be using it to access their registers