Kindle: Enable AutoSuspend plugin (#7612)

Kindles are not flagged canPowerOff, although that's technically not
entirely warranted, but sorta makes sense.

The Plugin already handles that sanely, and will only expose/honor the
suspend timer.

plugins/autosuspend.koplugin/main.lua

@@ -1,6 +1,7 @@
 local Device = require("device")
 
 if not Device:isCervantes() and
+    not Device:isKindle() and
     not Device:isKobo() and
     not Device:isRemarkable() and
     not Device:isSDL() and