ACPI: mark empty get_cst_entries() weak

This function prevents the linker from choosing the right
get_cst_entries(), preventing writing the _CST tables.

Change-Id: I4bc0168aee110171faeaa081f217dfd1536bb821
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/496
Tested-by: build bot (Jenkins)

src/arch/x86/include/arch/acpigen.h

@@ -66,6 +66,6 @@ int acpigen_write_resourcetemplate_footer(int len);
 int acpigen_write_mainboard_resource_template(void);
 int acpigen_write_mainboard_resources(const char *scope, const char *name);
 
-int get_cst_entries(struct cst_entry **) __attribute__((weak));
+int get_cst_entries(struct cst_entry **);
 
 #endif

src/cpu/intel/speedstep/acpi.c

@@ -62,7 +62,7 @@ static int get_fsb(void)
 	return 200;
 }
 
-int get_cst_entries(struct cst_entry **entries __attribute__((unused)))
+int __attribute__((weak)) get_cst_entries(struct cst_entry **entries __attribute__((unused)))
 {
 	return 0;
 }