[feat] Add Device:hasFewKeys() (#6193)

This will allow to behave subtly different in certain instances.
Cf. <https://github.com/koreader/koreader/issues/4029>.

frontend/device/generic/device.lua

@@ -29,6 +29,7 @@ local Device = {
     hasKeyboard = no,
     hasKeys = no,
     hasDPad = no,
+    hasFewKeys = no,
     hasWifiToggle = yes,
     hasWifiManager = no,
     isHapticFeedbackEnabled = no,

frontend/device/pocketbook/device.lua

@@ -217,6 +217,7 @@ local PocketBook515 = PocketBook:new{
     isTouchDevice = no,
     hasWifiToggle = no,
     hasDPad = yes,
+    hasFewKeys = yes,
 }
 
 -- PocketBoot 613 Basic
@@ -226,6 +227,7 @@ local PocketBook613 = PocketBook:new{
     isTouchDevice = no,
     hasWifiToggle = no,
     hasDPad = yes,
+    hasFewKeys = yes,
 }
 
 -- PocketBook Basic Lux 2
@@ -235,6 +237,7 @@ local PocketBook616 = PocketBook:new{
     isTouchDevice = no,
     hasWifiToggle = no,
     hasDPad = yes,
+    hasFewKeys = yes,
 }
 
 -- PocketBook Lux 4