spi: remove obsolete spi-ti-ssp driver

The tnetv107x platform is getting removed, so this driver
will not be needed any more.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>