tool: Move read_debug to trait so generic code can use it

Returns error for backends that don't support it.

tool/src/access/lpc/linux.rs

@@ -130,12 +130,6 @@ impl AccessLpcLinux {
         Ok(self.cmd.write(addr as u16, data)?)
     }
 
-    /// Read from the debug space
-    //TODO: better public interface
-    pub unsafe fn read_debug(&mut self, addr: u8) -> Result<u8, Error> {
-        Ok(self.dbg.read(addr as u16)?)
-    }
-
     /// Returns Ok if a command can be sent
     unsafe fn command_check(&mut self) -> Result<(), Error> {
         if self.read_cmd(SMFI_CMD_CMD)? == 0 {
@@ -180,4 +174,8 @@ impl Access for AccessLpcLinux {
     fn data_size(&self) -> usize {
         SMFI_CMD_SIZE - SMFI_CMD_DATA as usize
     }
+
+    unsafe fn read_debug(&mut self, addr: u8) -> Result<u8, Error> {
+        Ok(self.dbg.read(addr as u16)?)
+    }
 }