bootblock: Declare common bootblock_pre_c_entry routine

Enable uses of a common bootblock_pre_c_entry routine.  Pass in TSC
value as a uint64_t value.

TEST=Build for amenia and Galileo Gen2

Change-Id: I8be2e079ababb2cf1f9b7e6293f93e7c778761a1
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/15124
Tested-by: build bot (Jenkins)
Reviewed-by: Lee Leahy <lpleahyjr@gmail.com>

src/include/bootblock_common.h

@@ -29,6 +29,12 @@ void bootblock_mainboard_early_init(void);
 void bootblock_mainboard_init(void);
 void bootblock_soc_early_init(void);
 void bootblock_soc_init(void);
+
+/*
+ * C code entry point for the boot block.
+ */
+void asmlinkage bootblock_c_entry(uint64_t base_timestamp);
+
 /*
  * This is a the same as the bootblock main(), with the difference that it does
  * not collect a timestamp. Instead it accepts the first timestamp as an