Currently, PM domains can only support hierarchy for simple
providers (e.g. ones with #power-domain-cells = 0).

Add more generic support by creating an of_genpd helper which can
parse a nexus node map, and create domain hierarchy.

described in section 2.5.1 of the DT spec.

Signed-off-by: Kevin Hilman <khilman@baylibre.com>
---
Changes in v4:
- use new OF iterator for parsing map. See:
  https://lore.kernel.org/r/20251119-topic-lpm-of-map-iterator-v6-18-v1-1-1f0075d771a3@baylibre.com
- instead of mapping on probe, create of_genpd helper to be called by providers
- Link to v3: https://lore.kernel.org/r/20250613-pmdomain-hierarchy-onecell-v3-0-5c770676fce7@baylibre.com

Changes in v3:
- use of_parse_phandle_with_args_map() instead of custom parsing
- probe when device is attatched to PM domain
- Link to v2: https://lore.kernel.org/r/20250528-pmdomain-hierarchy-onecell-v2-0-7885ae45e59c@baylibre.com

Changes in v2:
- Use nexus map instead of creating new property as suggested by Rob H.
- Link to v1: https://lore.kernel.org/r/20250528-pmdomain-hierarchy-onecell-v1-1-851780700c68@baylibre.com

---
Kevin Hilman (TI.com) (2):
      pmdomain: core: support domain hierarchy via power-domain-map
      pmdomain: arm_scmi: add support for domain hierarchies

 drivers/pmdomain/arm/scmi_pm_domain.c | 11 ++++--
 drivers/pmdomain/core.c               | 64 ++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h             |  9 +++++
 3 files changed, 82 insertions(+), 2 deletions(-)
---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20250528-pmdomain-hierarchy-onecell-a46fad47d855
prerequisite-change-id: 20251119-topic-lpm-of-map-iterator-v6-18-a61447423adc:v1
prerequisite-patch-id: e2c4a8c727d0f172166cfa622e60d97048a97b26

Best regards,
--  
Kevin Hilman (TI.com) <khilman@baylibre.com>