remoteproc: cv1800b: Add initial support for C906L processor

This patch series introduces initial support for the C906L remote
processor in the Sophgo CV1800B SoC. The CV1800B SoC integrates multiple
cores, including a main application core running Linux, a C906L core
typically running RTOS, and an 8051 MCU.

The C906L is an asymmetric processor designed to typically run RTOS.
This patch adds the basic infrastructure to support remoteproc
management of the C906L processor, including firmware loading and basic
control (start/stop) from the main Linux core. Mailbox-related
functionality will be added in a separate patch, after Zephyr mainline
support for the C906L is ready [1].

The C906L remoteproc relies on the reset controller [1] to function
correctly [2].

A branch for testing is available at [3].

Link: zephyrproject-rtos/zephyr#69594 [1]
Link: https://lore.kernel.org/linux-riscv/[email protected] [2]
Link: https://github.com/pigmoral/linux/tree/cv1800b/rproc-test [3]

To: Bjorn Andersson <[email protected]>
To: Mathieu Poirier <[email protected]>
To: Rob Herring <[email protected]>
To: Krzysztof Kozlowski <[email protected]>
To: Conor Dooley <[email protected]>
To: Chen Wang <[email protected]>
To: Inochi Amaoto <[email protected]>
To: Junhui Liu <[email protected]>
To: Philipp Zabel <[email protected]>
To: Paul Walmsley <[email protected]>
To: Palmer Dabbelt <[email protected]>
To: Albert Ou <[email protected]>
To: Alexandre Ghiti <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]

---
Changes in v3:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v2: https://lore.kernel.org/r/[email protected]

Changes in v2:
- Add mbox-related properties in dt-bindings
- Remove reserved-memory node in dt examples
- Fix warnings in driver by handling conversions of `void *` and `void
  __iomem *` correctly
- Add missing <linux/bits.h> header
- Use `rproc_of_resm_mem_entry_init()` for vdev0buffer region
- Remove redundant rproc_shutdown in remove() function
- Link to v1: https://lore.kernel.org/r/[email protected]

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 3,
    "change-id": "20250527-cv1800-rproc-08b3a9d2e461",
    "prefixes": [],
    "history": {
      "v1": [
        "[email protected]"
      ],
      "v2": [
        "[email protected]"
      ]
    }
  }
}

Author: pigmoral