acpigen: make acpigen_write_len_f() non static

since it is used in CPU specific ACPI generation code

Change-Id: I2559658f43c89dc5b4dc8230dea8847d2802990c
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/947
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/arch/x86/boot/acpigen.c

@@ -35,7 +35,7 @@ static char *gencurrent;
 char *len_stack[ACPIGEN_LENSTACK_SIZE];
 int ltop = 0;
 
-static int acpigen_write_len_f(void)
+int acpigen_write_len_f(void)
 {
 	ASSERT(ltop < (ACPIGEN_LENSTACK_SIZE - 1))
 	    len_stack[ltop++] = gencurrent;

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

@@ -35,6 +35,7 @@ struct cst_entry {
 	int power;
 };
 
+int acpigen_write_len_f(void);
 void acpigen_patch_len(int len);
 void acpigen_set_current(char *curr);
 char *acpigen_get_current(void);