spi: txx9: Remove driver

CPU support for TX49xx is getting removed, so remove support SPI driver
for it.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: https://lore.kernel.org/r/20210105140305.141401-5-tsbogend@alpha.franken.de


Signed-off-by: Mark Brown <broonie@kernel.org>