powercap: intel_rapl: Allow interface drivers to configure rapl_defaults

powercap: intel_rapl: Allow interface drivers to configure rapl_defaults

RAPL default settings vary across different RAPL interfaces (MSR, TPMI,
MMIO). Currently, these defaults are stored in the common RAPL driver,
which requires interface-specific handling logic and makes the common
layer unnecessarily complex. There is no strong reason for the common
code to own these defaults, since they are inherently
interface-specific.

To prepare for moving default configuration into the individual
interface drivers,

 1. Move struct rapl_defaults into a shared header so that interface
    drivers can directly populate their own default settings.

 2. Change the @defaults field in struct rapl_if_priv from void * to
    const struct rapl_defaults * to improve type safety and readability
    and update the common driver to use the typed defaults structure.

 3. Update all internal getter functions and local pointers to use
    const struct rapl_defaults * to maintain const-correctness.

 4. Rename and export the common helper functions (check_unit,
    set_floor_freq, compute_time_window) so interface drivers may
    reuse or override them as appropriate.

No functional changes. This is a preparatory refactoring to allow
interface drivers to supply their own RAPL default settings.

Co-developed-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260212233044.329790-9-sathyanarayanan.kuppuswamy@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>