API: Use stack pointer as API signature search hint in the glue layer.

De-hardcode range in RAM we search for the API signature. Instead use the stack
pointer as a hint to narrow down the range in which the signature could reside
(it is malloc'ed on the U-Boot heap, and is hoped to remain in some proximity
from stack area). Adjust PowerPC code in API demo to the new scheme.

Signed-off-by: Rafal Czubak <rcz@semihalf.com>
Signed-off-by: Rafal Jaworowski <raj@semihalf.com>
diff --git a/api_examples/glue.h b/api_examples/glue.h
index a82f783..0adb8b3 100644
--- a/api_examples/glue.h
+++ b/api_examples/glue.h
@@ -30,12 +30,12 @@
 #ifndef _API_GLUE_H_
 #define _API_GLUE_H_
 
-#define API_SEARCH_START	(255 * 1024 * 1024)	/* start at 1MB below top RAM */
-#define API_SEARCH_END		(256 * 1024 * 1024 - 1)	/* ...and search to the end */
+#define API_SEARCH_LEN		(3 * 1024 * 1024)	/* 3MB search range */
 
-int	syscall(int, int *, ...);
-void *	syscall_ptr;
+extern void *syscall_ptr;
+extern uint32_t search_hint;
 
+int	syscall(int, int *, ...);
 int	api_search_sig(struct api_signature **sig);
 
 /*