rockchip: puma-rk3399: add button support

The Haikou Devkit exposes 4 buttons over GPIO so let's enable their
support so their status can be queried from the `button` command from
the CLI.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/puma-rk3399_defconfig b/configs/puma-rk3399_defconfig
index 5319239..bc9a791 100644
--- a/configs/puma-rk3399_defconfig
+++ b/configs/puma-rk3399_defconfig
@@ -56,6 +56,8 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_SYS_MMC_ENV_DEV=1
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+CONFIG_BUTTON=y
+CONFIG_BUTTON_GPIO=y
 CONFIG_GPIO_HOG=y
 CONFIG_SPL_GPIO_HOG=y
 CONFIG_ROCKCHIP_GPIO=y