Integrate u-boot-seco-imx/seco_lf_v2021.04-gm_d18_rtc

Commit: https://git.seco.com/edgehog/bsp/nxp/u-boot-seco-imx/-/commit/67f8d7f9a01abada972d4ba58c0d27eece6cc935

[D18] setup RTC PMIC voltage

Raise RTC PMIC voltage from 1.8V a 1.85V to better stay within spec.