fix: assumptions about synthesizable code

feat: add initial test for spi peripheral

feat: add test for lsbfirst

chore: remove todo comments

feat: add csn pulse test and rx, tx disabling test

feat: add tests for rx blocking

chore: move spi models to separate file

feat: add tests for clock phase, polarity

feat: tests for multiple transmissions, rx lost

chore: add ghdl support vhdl2008 arg

feat: add first basic test

chore: few updates

feat: implement initial hdl_spi