dt-bindings: input: ti,twl4030-keypad: convert to DT schema

dt-bindings: input: ti,twl4030-keypad: convert to DT schema

Convert the legacy TXT binding for the TWL4030 keypad module
to the modern YAML DT schema format. This adds formal validation
and improves documentation by inheriting from the matrix-keymap schema.

Signed-off-by: Jihed Chaibi <jihed.chaibi.dev@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250819222823.157943-1-jihed.chaibi.dev@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>