tests: drivers: spi: spi_loopback: Added mimxrt1170_evk_cm7

Added overlay inside the spi loopback test for the
mimxrt1170_evk_cm7, enabled DMA and Async by default.
Added testcase for async and dma.

Signed-off-by: Emilio Benavente <emilio.benavente@nxp.com>