Convert CONFIG_KEYBOARD to Kconfig

This converts the following to Kconfig:
   CONFIG_KEYBOARD

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
index 7f3aee5..10301c1 100644
--- a/arch/arm/mach-exynos/Kconfig
+++ b/arch/arm/mach-exynos/Kconfig
@@ -23,6 +23,7 @@
 	imply CMD_HASH
 	imply CRC32_VERIFY
 	imply HASH_VERIFY
+	imply KEYBOARD
 	imply USB_ETHER_ASIX
 	imply USB_ETHER_RTL8152
 	imply USB_ETHER_SMSC95XX