spi_nxp_lpspi: Use default RTIO submit

For the CPU-based drivers, delete the old MCUX based RTIO driver and use
the default RTIO submit implementation instead.

Rationale:
- 300 LOC -> 1 LOC to maintain.
- MCUX SDK based driver cannot control the chip select for the transfer
  properly, but the new spi_nxp_lpspi.c driver can. So this fixes the
  bug with the PCS when using RTIO.

Also enable the default RTIO implementation for DMA based driver.
In the future a DMA based RTIO driver with custom implementation can be
designed, but for CPU based transfer, which is already not optimal
performance, code maintenance is more important. Only requirement is
asynchronous submit, which is accomplished by p4wq in rtio workq.

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