MIPS: remove CONFIG_SYS_MHZ

Resolve all uses of CONFIG_SYS_MHZ with the currently defined value.
Remove code which depends on CONFIG_SYS_MHZ but where no board configs
actually use that code.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/mach-jz47xx/include/mach/jz4780.h b/arch/mips/mach-jz47xx/include/mach/jz4780.h
index 4422e50..880445d 100644
--- a/arch/mips/mach-jz47xx/include/mach/jz4780.h
+++ b/arch/mips/mach-jz47xx/include/mach/jz4780.h
@@ -60,7 +60,7 @@
 
 /* PLL setup */
 #define JZ4780_SYS_EXTAL	48000000
-#define JZ4780_SYS_MEM_SPEED	(CONFIG_SYS_MHZ * 1000000)
+#define JZ4780_SYS_MEM_SPEED	(1200 * 1000000)
 #define JZ4780_SYS_MEM_DIV	3
 #define JZ4780_SYS_AUDIO_SPEED	(768 * 1000000)