spi_nxp_lpspi: Fix S32 regressions

There are two bugs that caused regression for S32:

First there is a silicon errata specifically for the mask version on
this board that causes FIFO flush to not work as expected. The
workaround is to do a module reset before each transfer.

Second there was a division error for word size > 1 byte. The division
should be rounded up, not down, otherwise there will be an infinite
interrupt loop because the TX fifo will not be written to but the TDR
interrupt enabled causes interrupt when TX fifo is empty.

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