tests: spi_loopback: Add delay props to RT series

RT series have LPSPI data input setup and hold requirements and CS lead/lag
requirements not being met on the current configuration for this
test, causing flaky data transfer on CPHA 0 and 2 tests.
Fix by adding delay properties.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>