spi_mcux_lpspi: More precise configuration checks

These changes:
* Fix the check of the word size to be more useful
  - check min frame size instead of max
  - check for min word size requirement
  - add a clarifying comment about what the word size represents in
    hardware since the nomenclature from zephyr does not match the nxp
    references
* Add a clarifying comment about half duplex being supported by hardware
* Add LPSPI_ namespace to defines
* Change chip select error message to be more clear about the problem
* Move the check of the clock device being ready to the lpspi init,
  instead of checking it every time on configure. It probably also makes
  more sense to not ready the lpspi device if the clock is not ready.
* Move the bare-metal configuration of bit fields AFTER the SDK Init
  call.
* Return the proper error code if clock control call errors.

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