arm64: dts: imx8mp-evk: Add vpcie3v3aux regulator for PCIe M.2 connector

arm64: dts: imx8mp-evk: Add vpcie3v3aux regulator for PCIe M.2 connector

Refer to PCI Express M.2 Specification r5.1 sec3.1.1 Power Sources and
Grounds.

PCI Express M.2 Socket 1 utilizes a 3.3 V power source. The voltage
source, 3.3 V, is expected to be available during the system’s
stand-by/suspend state to support wake event processing on the
communications card.

Add vpcie3v3aux regulator to let this 3.3 V power source always on for
PCIe M.2 Key E connector on i.MX8MP EVK board.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>