arm64: dts: imx8mp-somdevices.dtsi: Configure memory and allocate less cma memory.

arm64: dts: imx8mp-somdevices.dtsi: Configure memory and allocate less cma memory.
Based on:
https://github.com/nxp-imx/linux-imx/commit/910178d16dd3e4cba08bebde148c493308cd3fd7
https://git.toradex.com/cgit/linux-toradex.git/commit/arch/arm64/boot/dts/freescale/imx8mp-verdin.dtsi?h=toradex_5.15-2.2.x-imx&id=5442dba1b301ab623abc8badf1c5a1dc4f851756
https://git.toradex.com/cgit/linux-toradex.git/commit/arch/arm64/boot/dts/freescale/imx8mp-verdin.dtsi?h=toradex_5.15-2.2.x-imx&id=177b4e0e45cce067933a416f674991f7ed279924

Signed-off-by: Josep Orga <jorga@somdevices.com>