arm64: dts: add NXP i.MX8MM-EVKB support

Add the i.MX8MM-EVKB [1] devicetree support. The EVKB is basically the
same device except for the different used PMIC.

[1] https://www.nxp.com/design/development-boards/ \
        i-mx-evaluation-and-development-boards/ \
	evaluation-kit-for-the-i-mx-8m-mini-applications-processor:8MMINILPD4-EVK

Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
[m.felsch@pengutronix.de: Adapt the commit message]
[m.felsch@pengutronix.de: Include Shawns feedback]
[m.felsch@pengutronix.de: Fix the regulator settings]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>