Revert "spi: cadence: Fix encoded CS mode"

This reverts commit eff2ab05a41f65e52679e630da7d5046a69bc4bc.
spi: cadence: Fix 3-to-8 mux mode

In 3-to-8 mux mode for the CS pins we need to set the PERI_SEL bit in the
control register. Currently the driver never sets this bit even when
configured for 3-to-8 mux mode. This patch adds code which sets the bit
during device initialization when necessary.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>