x86/resctrl: Move rdt_find_domain() to be visible to arch and fs code

x86/resctrl: Move rdt_find_domain() to be visible to arch and fs code

rdt_find_domain() finds a domain given a resource and a cache-id.  This is
used by both the architecture code and the filesystem code.

After the filesystem code moves to live in /fs/, this helper is either
duplicated by all architectures, or needs exposing by the filesystem code.

Add the declaration to the global header file. As it's now globally visible,
and has only a handful of callers, swap the 'rdt' for 'resctrl'. Move the
function to live with its caller in ctrlmondata.c as the filesystem code will
not have anything corresponding to core.c.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Amit Singh Tomar <amitsinght@marvell.com> # arm64
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com> # arm64
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20250311183715.16445-13-james.morse@arm.com