boards: mr_canhubk3: enable LPUART serial driver

Reuse existing MCUX-based shim driver for LPUART that is compatible with
the hardware block in S32K344. DMA is not yet supported.

Use the board's debug connector (P6 / LPUART2) as default console.

Signed-off-by: Manuel Argüelles <manuel.arguelles@nxp.com>