Finish conversion of CONFIG_SYS_CLK_FREQ to Kconfig

In order to finish moving this symbol to Kconfig for all platforms, we
need to do a few more things.  First, for all platforms that define this
to a function, introduce CONFIG_DYNAMIC_SYS_CLK_FREQ, similar to
CONFIG_DYNAMIC_DDR_CLK_FREQ and populate clock_legacy.h.  This entails
also switching all users from CONFIG_SYS_CLK_FREQ to get_board_sys_clk()
and updating a few preprocessor tests.

With that done, all platforms that define a value here can be converted
to Kconfig, and a fall-back of zero is sufficiently safe to use (and
what is used today in cases where code may or may not have this
available).  Make sure that code which calls this function includes
<clock_legacy.h> to get the prototype.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/xtfpga.h b/include/configs/xtfpga.h
index d1ba78a..c8a6e9a 100644
--- a/include/configs/xtfpga.h
+++ b/include/configs/xtfpga.h
@@ -22,12 +22,6 @@
 
 #define CONFIG_XTFPGA
 
-/* FPGA CPU freq after init */
-#ifndef __ASSEMBLY__
-unsigned long get_board_sys_clk(void);
-#endif
-#define CONFIG_SYS_CLK_FREQ		get_board_sys_clk()
-
 /*===================*/
 /* RAM Layout        */
 /*===================*/
@@ -172,7 +166,7 @@
 #define CONFIG_SYS_NS16550_COM1		IOADDR(0x0D050020) /* Base address */
 
 /* Input clk to NS16550 (in Hz; the SYS_CLK_FREQ is in kHz) */
-#define CONFIG_SYS_NS16550_CLK		CONFIG_SYS_CLK_FREQ
+#define CONFIG_SYS_NS16550_CLK		get_board_sys_clk()
 
 /*======================*/
 /* Ethernet Driver Info */