spi: cadence: Add dependency on ARM

Add dependency on ARM in Kconfig.
This is to fix the build error related to _relaxed IO.
Remove dependency on SPI_MASTER because this is already defined
under if SPI_MASTER in Kconfig.

Signed-off-by: Harini Katakam <harinik@xilinx.com>
Signed-off-by: Mark Brown <broonie@linaro.org>