drivers: spi: spi_nrfx_spi: Add CPOL handling on SCK pin

Pin state after SPI deinitialization is based on pinctrl configuration.
On the other hand, CPOL is set during runtime. When the SPI instance
is disabled GPIO takes control over SCK and drives it to state set
by pinctrl driver. This might causes an invalid SCK state
when the transaction is configured with CPOL (Clock Polarity).

To address this issue, a patch was introduced to the SPI driver.
Now, when a SPI instance is configured with CPOL,
the driver is setting in the runtime the correct state of the SCK pin.

Signed-off-by: Adam Wojasinski <adam.wojasinski@nordicsemi.no>