Use new `svd2rust` functionality targeted at RISC-V devices

[jessebraham]

svd2rust has added some new functionality specific to RISC-V devices, see:

• RISC-V: adoption of riscv-pac rust-embedded/svd2rust#786
• Use riscv section for RISC-V targets rust-embedded/svd2rust#856

An example of this functionality being applied to a PAC can be seen here:

• using new fork of svd2rust greenlsi/e310x#1

We should take advantage of these new features and add settings.yaml files for each RISC-V PAC.

[romancardenas]

Here the e310x pac is generated using svd2rust 0.34.0. You can have an idea about how to use the standard CLINT implementation with the settings.yaml file.