This is much, _much_ faster than __tinygo_spi_transfer which can only
transfer a single byte at a time. This is especially important for
simulated displays.
I've already implemented the browser side of this on the playground and
have used this patch for local testing where it massively speeds up
display operations.
This makes the code a bit cleaner because ErrTxInvalidSliceSize isn't
redefined in every file that uses SPI and Mode0/Mode1/Mode2/Mode3 is
defined for every target that uses SPI.
deadprogram
dkegel-fastly
Ayke van Laethem
Yurii Soldak