sandbox: Enable USB keyboard

Enable the USB keyboard on sandbox, now that we have a suitable emulation
driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 4053848..0178674 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -63,6 +63,8 @@
 CONFIG_DM_USB=y
 CONFIG_USB_EMUL=y
 CONFIG_USB_STORAGE=y
+CONFIG_USB_KEYBOARD=y
+CONFIG_SYS_USB_EVENT_POLL=y
 CONFIG_SYS_VSNPRINTF=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_TPM=y