arm: zynq: Move ZYNQ_SERIAL to Kconfig

Move cadence/zynq serial driver via Kconfig

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/zynq_cc108_defconfig b/configs/zynq_cc108_defconfig
index 6fe20ba..fcf4635 100644
--- a/configs/zynq_cc108_defconfig
+++ b/configs/zynq_cc108_defconfig
@@ -44,6 +44,7 @@
 CONFIG_DEBUG_UART_BASE=0xe0000000
 CONFIG_DEBUG_UART_CLOCK=50000000
 CONFIG_DEBUG_UART_ANNOUNCE=y
+CONFIG_ZYNQ_SERIAL=y
 CONFIG_ZYNQ_QSPI=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y