spi_mcux_lpspi: Move RTIO code to rtio functions

To facilitate changing this driver, decouple rtio from functions not
specific to RTIO. This also requires moving the sdk driver handle
creation outside of the configure call. An effect of this is we can
stop initializing an unused sdk driver handle for the dma path.

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