[feat, UX] bump base for SDL2: preliminary gamepad support (#3819)

* [feat] SDL2: preliminary gamepad support https://github.com/koreader/koreader-base/pull/628

This is a "dumb" implementation that spits out fake keyboard events.

* Left stick & d-pad: arrow keys
* Bumpers and right stick: page up/down
* Menu button: menu
* A: enter
* B: back

This is sufficient to use most of the program.

Made possible by @onde2rock's recent efforts in https://github.com/koreader/koreader/pull/3796
https://github.com/koreader/koreader/pull/3785 https://github.com/koreader/koreader/pull/3774
https://github.com/koreader/koreader/pull/3765 and https://github.com/koreader/koreader/pull/3745

base

@@ -1 +1 @@
-Subproject commit 2ecc6d1134ae94053653924648d7a04945428616
+Subproject commit 266628d635da0ffa06ec30f2dd85388136beecc5