drivers: spi: nrfx_spi(m/s): enable cross domain pins for nRF54L15

SPI(M/S)20 and SPIM(M/S)21 instances enable usage of pins on different
port, but require request for constant latency mode. Added
handling of such scenario in the driver. Added testcase
to cover it.

Signed-off-by: Michał Stasiak <michal.stasiak@nordicsemi.no>