arm64: dts: imx8ulp: increase the clock speed of LPSPI

LPSPI transfer max speed is half of the root clock.
Increase the root clock speed to support faster data transmission.

And update the parent clock of all i2c/spi with IMX8ULP_CLK_FROSC_DIV2
which could produce accurate clock for i2c/spi usage.

Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Jun Li <jun.li@nxp.com>
Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>