rpi: Enable USB keyboard support

This is currently disabled, so USB keyboards are not detected in U-Boot.
Enable this option to fix that.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Jonathan Gray <jsg@jsg.id.au>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Paul Barker <pbarker@toganlabs.com>
diff --git a/configs/rpi_defconfig b/configs/rpi_defconfig
index 6b3cec5..eaf9bb9 100644
--- a/configs/rpi_defconfig
+++ b/configs/rpi_defconfig
@@ -15,6 +15,7 @@
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_USB=y
+CONFIG_DM_KEYBOARD=y
 CONFIG_DM_MMC=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_BCM2835=y