Added SPI support. Now working using the loopback feature (UCLISTEN bit).

Also fixed a relocation error problem due to packed structures and placement
of instantiations in text page via "const static ...".  No change to text
or data page sizes at compilation.  Since msp430_usci_xxx_t will never be on
the stack, removal of the packed attribute was the way to work around what
appears to be a compiler problem.