Update to LVGL master (unl0kr)

Fixes: #25 (closed)

This compiles and runs now. I chose the quick intermediate way of just adapting the libinput driver in our lv_drivers fork to the new lvgl API: https://github.com/calebccff/lv_drivers/pull/6

This is a stopgap because eventually we'll need to bring our fork back into lvgl.

Left to do before this can land:

• Implement the direct rendering quirk for the new fbdev driver (the code is currently commented out: https://github.com/lvgl/lvgl/blob/master/src/drivers/display/fb/lv_linux_fbdev.h). Done except for landing and consuming https://github.com/lvgl/lvgl/pull/5444.
• Restore idle shutdown (https://github.com/lvgl/lvgl/issues/5443 / https://github.com/lvgl/lvgl/pull/5463)
• Restore key border coloring (https://github.com/lvgl/lvgl/issues/5442)