riscv: Add driver for the cvitek reset controller

[bnovkov]

Summary

This patch adds support for the cvitek reset controller.
This controller is present on the Milk-V riscv SoCs. The controller is
currently used by the if_dwc driver.

[imp]

sys/riscv/cvitek/cvitek_reset.c

65

If we use a table, then we can make this a module that's automatically loaded by the loader when it finds it in the FDT.
Though if it's not a module, this is fine for now.

[jrtc27]

sys/riscv/cvitek/cvitek_reset.c

83

Uh, who knows what this is going to pick up... surely there's a phandle reference? That's how this normally works... that or it's a child of the syscon.

104–105

By definition these are both just 32? Don't see what benefit the calculation gives when it's already hard-coded in the type name.

[bnovkov]

Address @jrtc27 's comments.

[bnovkov]

sys/riscv/cvitek/cvitek_reset.c

65

It is not a module for now, but I'll bear this in mind, thanks!

83

yeah, this was an issue in other places as well, I've rearranged the dts to include a syscon phandle and updated the code accordingly.

104–105

Right, unnecessary, replaced it with a constant.