With this commit no direct register access to SPI hardware should be done anymore for Teensy LC. This is done in the same way as for Teensy 4. Additionally the USE_TEENSY4_SPI define was renamed to USE_SPI_LIB as it is now used for not only Teensy 4.

-added T4 aware functions
-chenged transfer from polling to internal DMA (blocking mode)

(attention, untested)