f5510/spi: Add support for F5510 ext (USCI A0/B0)

64-pin and 80-pin MSP430F5510 pinouts add two additional USCIs, which
are supported with a compilation definition, MSP430F5510_EXT. This
allows dynamic inclusion of the featureset depending on which device is
in use.
*/spi: Resolved SPI library bug - missing breaks

Break statements were somehow missing in the SPI libraries. This would
cause "falling through" the switch function unintentionally.
msp430/tlc5925: Added tlc5925 library
msp/tlc5925: Include changes and other minor mods

Change includes to work with the relative structure that has been
established. This will allow the use of the TLC5925 library with any
supported MSP430 device.