Convert CONFIG_KEYBOARD to Kconfig

This converts the following to Kconfig:
   CONFIG_KEYBOARD

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/novena_defconfig b/configs/novena_defconfig
index 06864db..e40e80e 100644
--- a/configs/novena_defconfig
+++ b/configs/novena_defconfig
@@ -60,6 +60,7 @@
 CONFIG_SYS_I2C_LEGACY=y
 CONFIG_SPL_SYS_I2C_LEGACY=y
 CONFIG_SYS_I2C_MXC=y
+CONFIG_KEYBOARD=y
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y