arm: qemu: Enable usb keyboard as an input device

Commit 02be57caf730 ("riscv: qemu: Enable usb keyboard as an input
device") adds PCI xHCI support to QEMU RISC-V virtual machines and
enables using a USB keyboard as one of the input devices. Similarly,
enable those for ARM virtual machines as well.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
diff --git a/board/emulation/qemu-arm/qemu-arm.env b/board/emulation/qemu-arm/qemu-arm.env
index 86a99a2..fb4adef 100644
--- a/board/emulation/qemu-arm/qemu-arm.env
+++ b/board/emulation/qemu-arm/qemu-arm.env
@@ -2,7 +2,7 @@
 
 /* environment for qemu-arm and qemu-arm64 */
 
-stdin=serial
+stdin=serial,usbkbd
 stdout=serial,vidconsole
 stderr=serial,vidconsole
 fdt_high=0xffffffff