soc/intel/cannonlake: remove top_of_32bit_ram() declaration

It should never be globally exposed. Remove it.

Change-Id: I90e201ddd4df2cda89e7d3e4cb81bdc2a81cac83
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/20583
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/intel/cannonlake/include/soc/systemagent.h

@@ -98,7 +98,4 @@
 /* System Agent identification */
 u8 systemagent_revision(void);
 
-/* Top of 32bit usable memory */
-u32 top_of_32bit_ram(void);
-
 #endif