drivers: spi: nrf: add support for spim12x instances

SPIM12x instances can perform DMA only from memory region
that is cacheable by default.
SPIM12x instances pins are configured via CTRLSEL mechanism,
which prevents the GPIO registers from ensuring correct bus
state when peripheral does not drive the bus lines.
External configuration of SPIM12x ENABLE register fixes this issue.

Signed-off-by: Nikodem Kastelik <nikodem.kastelik@nordicsemi.no>