tests: spi_loopback: Add arduino overlay for CS test

Add overlay for arduino r3 for the CS testing enablement of the test.

Since I do not know the hardware range situations of all the vendors,
for now I just put this as a platform_allow for two different version
LPSPI platforms. RT1050 has LPSPI v1 and MCXN has LPSPI v2. On MCXN,
lower the SPI priority to let the GPIO interrupt process in time.

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