imx: power-domain: Get rid of SMCCC dependency

This driver is the only SMCCC dependency in iMX8M U-Boot port. Rework
the driver based on Linux GPCv2 driver to directly control the GPCv2
block instead of using SMCCC calls. This way, U-Boot can operate the
i.MX8M power domains without depending on anything else.

This is losely based on Linux GPCv2 driver. The GPU, VPU, MIPI power
domains are not supported to save space, since they are not useful in
the bootloader. The only domains kept are ones for HSIO, PCIe, USB.

Tested-By: Tim Harvey <tharvey@gateworks.com> #imx8mp-venice-defconfig
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>