refactor: adopt virtual-ID ABI and per-device context for SCMI protocols

[agicy]

Summary

Refactor the virtio-scmi implementation to replace the phandle-based ABI with a virtual-ID ABI, and move from global protocol registration to per-device context. This prepares the way for multi-device SCMI support and eliminates dependencies on static phandle values.

Driver changes (driver/)

• Split monolithic scmi_server.c into per-protocol files under driver/virtio/scmi/{server,clock,power,reset}.c. Each protocol is independently initialized from the hvisor DT node's clocks/resets/ power-domains properties using of_count_phandle_with_args().
• Virtual-ID ABI: Clock, reset, and power domains are identified by their index in the hvisor device tree node, not by phandle. The old SET_PHANDLE ioctl subcommands are removed.
• Lifecycle helpers: hvisor_scmi_init() / hvisor_scmi_cleanup() provide symmetric init/teardown with proper error-path rollback.
• Resource caching: Clock and reset controls are cached after first lookup (of_clk_get / __of_reset_control_get) and released at module exit, avoiding repeated DT traversals.
• Deleted reset-domains.c: The old dynamic reset-controller walk was replaced by direct DT property access, matching the approach used for clocks and power domains.

Tools changes (tools/)

• Per-device protocol registration: Replaced the global scmi_protocol table with scmi_dev_register_protocol(), storing protocol handlers in SCMIDev. This allows multiple SCMI device instances with different protocol sets.
• ID arrays instead of phandle/map: JSON config now uses direct clock_ids/reset_ids/power_ids arrays instead of *_phandle + *_max_num + allowed_list + *_map. The wildcard "*" syntax is replaced by explicit ID enumeration.
• scmi_resp_ctx for safe response buffer tracking: all protocol handlers now use scmi_resp_write() to advance a write cursor, catching buffer overflows at write time.
• Unified ioctl helper: hvisor_scmi_ioctl_cmd() uses the persistent ko_fd (opened once in virtio_start()), removing repeated open/close of /dev/hvisor.
• Conditional compilation removed: ENABLE_VIRTIO_SCMI is gone — SCMI is always compiled in, reducing build complexity.

Compatibility

All kernel APIs used (genpd_dev_pm_attach_by_id, __of_reset_control_get, etc.) are available since Linux v5.1 or earlier. The code builds and runs on Linux 6.1 without regression.

References

Closes: #106, #107.
Refactor: #84.