spi: cadence_qspi: Migrate CONFIG_CQSPI_REF_CLK to Kconfig

This is a little tricky since SoCFPGA has code to determine this as
runtime.  Introduce a guard variable for platforms to select if they
have a static value to use.  Then for ARCH_SOCFPGA, call
cm_get_qspi_controller_clk_hz() and otherwise continue the previous
behavior.

Cc: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/k2g_evm_defconfig b/configs/k2g_evm_defconfig
index 440a76f..251a982 100644
--- a/configs/k2g_evm_defconfig
+++ b/configs/k2g_evm_defconfig
@@ -89,6 +89,8 @@
 CONFIG_SPI=y
 CONFIG_DM_SPI=y
 CONFIG_CADENCE_QSPI=y
+CONFIG_HAS_CQSPI_REF_CLK=y
+CONFIG_CQSPI_REF_CLK=384000000
 CONFIG_DAVINCI_SPI=y
 CONFIG_USB=y
 CONFIG_DM_USB_GADGET=y