Convert CONFIG_CPU_FREQ_HZ to Kconfig

This converts the following to Kconfig:
   CONFIG_CPU_FREQ_HZ

Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/xilinx_zynqmp_r5_defconfig b/configs/xilinx_zynqmp_r5_defconfig
index a9c3c4a..98f46cf 100644
--- a/configs/xilinx_zynqmp_r5_defconfig
+++ b/configs/xilinx_zynqmp_r5_defconfig
@@ -9,6 +9,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="zynqmp-r5"
 CONFIG_DEBUG_UART_BASE=0xff010000
 CONFIG_DEBUG_UART_CLOCK=100000000
+CONFIG_CPU_FREQ_HZ=500000000
 CONFIG_DEBUG_UART=y
 CONFIG_SYS_LOAD_ADDR=0x0
 CONFIG_BOOTSTAGE=y