arm64: dts: imx8mp-phyboard-pollux: Add VCC_5V_SW regulator

Add fixed  regulator VCC_5V_SW based on the phyBOARD-Pollux schematics
to reflect the connectivity on the phyBOARD-Pollux-i.MX8MP.

Signed-off-by: Yashwanth Varakala <y.varakala@phytec.de>
Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Reviewed-by: Yannic Moog <y.moog@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>