boards/soc: nxp: MCXA, imxrt11xx: reconfigure clock source of lpspi

In spi loopback test, high bandrate is 16Mbps while some source of lpspi
are too low to support this bandrate. According the reference mannual,
to support 16Mbps, Input frequency at least should be 2*16MHz.
Update LPSPI input freq to maximum to get more accurate band rate
because band rate must be divisible by input freq.

Signed-off-by: Raymond Lei <raymond.lei@nxp.com>