acpid: expose empty /thermal and /power directories

redbear-upower reads /scheme/acpi/power/{adapters,batteries} and thermald
reads /scheme/acpi/thermal/ to enumerate power sources and thermal
zones. The acpid scheme previously only registered /scheme/acpi/{tables,
symbols}, so those paths returned ENOENT and both daemons logged a
warning then served an empty surface.

Add Thermal and Power as empty-directory HandleKind variants in the
TopLevel entries. thermald and redbear-upower both already treat an
empty directory as 'no devices', which is the correct fallback for
desktops and headless QEMU. The actual ACPI _TZ/_PR iteration that
would populate these is not yet wired into this fork; this change
removes the spurious warnings without claiming feature parity.

drivers/acpid/src/scheme.rs

@@ -43,6 +43,16 @@ enum HandleKind<'a> {
     Symbol { name: String, description: String },
     SchemeRoot,
     RegisterPci,
+    /// `/scheme/acpi/thermal` — always present, currently empty. The
+    /// ACPI `_TZ` namespace iteration that would populate it has not
+    /// been wired into this fork yet; thermald and `redbear-info` both
+    /// treat an empty directory as "no zones, serve empty surface".
+    Thermal,
+    /// `/scheme/acpi/power` — same story: UPower (and friends) probe
+    /// `power/adapters/` and `power/batteries/`. Empty directory means
+    /// "no ACPI-listed power sources on this machine", which is the
+    /// correct fallback for desktops/headless QEMU.
+    Power,
 }
 
 impl HandleKind<'_> {
@@ -55,6 +65,7 @@ impl HandleKind<'_> {
             Self::Symbol { .. } => false,
             Self::SchemeRoot => false,
             Self::RegisterPci => false,
+            Self::Thermal | Self::Power => true,
         }
     }
     fn len(&self, acpi_ctx: &AcpiContext) -> Result<usize> {
@@ -67,6 +78,7 @@ impl HandleKind<'_> {
             Self::Symbol { description, .. } => description.len(),
             // Directories
             Self::TopLevel | Self::Symbols(_) | Self::Tables => 0,
+            Self::Thermal | Self::Power => 0,
             Self::SchemeRoot | Self::RegisterPci => return Err(Error::new(EBADF)),
         })
     }
@@ -197,6 +209,8 @@ impl SchemeSync for AcpiScheme<'_, '_> {
                     [""] => HandleKind::TopLevel,
                     ["register_pci"] => HandleKind::RegisterPci,
                     ["tables"] => HandleKind::Tables,
+                    ["thermal"] => HandleKind::Thermal,
+                    ["power"] => HandleKind::Power,
 
                     ["tables", table] => {
                         let signature = parse_table(table.as_bytes()).ok_or(Error::new(ENOENT))?;
@@ -332,7 +346,9 @@ impl SchemeSync for AcpiScheme<'_, '_> {
 
         match &handle.kind {
             HandleKind::TopLevel => {
-                const TOPLEVEL_ENTRIES: &[&str] = &["tables", "symbols"];
+                const TOPLEVEL_ENTRIES: &[&str] = &[
+                    "tables", "symbols", "thermal", "power",
+                ];
 
                 for (idx, name) in TOPLEVEL_ENTRIES
                     .iter()