x86/mtrr: Rename mtrr_overwrite_state() to guest_force_mtrr_state()

Rename the helper to better reflect its function.

Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Link: https://lore.kernel.org/all/20241202073139.448208-1-kirill.shutemov%40linux.intel.com