arm64: dts: ti: am654-base-board: Add gpio_keys node

There are 2 push buttons: SW5 and SW6 that are basically connected to
WKUP_GPIO0_24 and WKUP_GPIO0_27 respectively. Add the respective
nodes and the pinctrl data to set the mode to GPIO and Input.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>