arm64: dts: ti: k3-am62-main: rm lpm region from dmsc

Remove the "lpm" region from am62-main DT and rather have it in the
lpmdemo DT since Low Power Mode is currently said to be supported only
using k3-am625-sk-lpmdemo
This will help fix the k3_r5_rproc: probe issues

Signed-off-by: Dhruva Gole <d-gole@ti.com>