spi: dw: Convert to generalized SPI controller API

Convert to generalized SPI controller API introduced by the
commit 8caab75f ("spi: Generalize SPI "master" to "controller"").
Inside driver variable name "master" is still used to indicate the driver
is master only.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>