serial: lpuart: restructure lpuart driver

serial: lpuart: restructure lpuart driver

Drop CONFIG_LPUART_32B_REG.
Move the register structure to a common file include/fsl_lpuart.h
Define lpuart_serial_platdata structure which includes the reg base and flags.
For 32Bit register access, use lpuart_read32/lpuart_write32 which handles
big/little endian.
For 8Bit register access, still use the orignal code.

Signed-off-by: Peng Fan <[email protected]>
Reviewed-by : Stefano Babic <[email protected]>
Cc: Bhuvanchandra DV <[email protected]>
Cc: York Sun <[email protected]>
Cc: Shaohui Xie <[email protected]>
Cc: Alison Wang <[email protected]>