x86,fs/resctrl: Use struct rdt_domain_hdr when reading counters

x86,fs/resctrl: Use struct rdt_domain_hdr when reading counters

Convert the whole call sequence from mon_event_read() to resctrl_arch_rmid_read() to
pass resource independent struct rdt_domain_hdr instead of an L3 specific domain
structure to prepare for monitoring events in other resources.

This additional layer of indirection obscures which aspects of event counting depend
on a valid domain. Event initialization, support for assignable counters, and normal
event counting implicitly depend on a valid domain while summing of domains does not.
Split summing domains from the core event counting handling to make their respective
dependencies obvious.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/20251217172121.12030-1-tony.luck@intel.com