Convert CONFIG_SYS_TIMER_COUNTS_DOWN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_TIMER_COUNTS_DOWN

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/xilinx_zynq_virt_defconfig b/configs/xilinx_zynq_virt_defconfig
index 1db3a2c..a4c555d 100644
--- a/configs/xilinx_zynq_virt_defconfig
+++ b/configs/xilinx_zynq_virt_defconfig
@@ -146,6 +146,7 @@
 CONFIG_CI_UDC=y
 CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_USB_FUNCTION_THOR=y
+CONFIG_SYS_TIMER_COUNTS_DOWN=y
 CONFIG_SPL_GZIP=y
 CONFIG_EFI_RUNTIME_UPDATE_CAPSULE=y
 CONFIG_EFI_CAPSULE_FIRMWARE_RAW=y