drm/imagination: Use dev_pm_domain_attach_list()

drm/imagination: Use dev_pm_domain_attach_list()

This helper handles the attaching and linking of the entire list of power
domains. Besides making pvr_power_domains_init() simpler, this also lays
the groundwork to simplify supporting the varied power domain names used in
Volcanic GPU cores.

Note that we still need to create the links between power domains to ensure
they're brought up in a valid sequence.

Reviewed-by: Alessio Belle <alessio.belle@imgtec.com>
Link: https://patch.msgid.link/20260123-pm-domain-attach-list-v1-1-d51dd7e43253@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>