Merge branch 'next' of https://gitlab.denx.de/u-boot/custodians/u-boot-riscv into next

- Disable CMD_IRQ for RISC-V.
- Update sipeed/maix doc
- Obtain reg of SiFive RAM via dev_read_addr_index() instead of regmap API.
- Cleans up RISC-V timer drivers and converts them to DM.
- Correctly handle IPIs already pending upon prior stage bootloader (on the K210)