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.c b/api_examples/glue.c
index 2bf47ae..200b163 100644
--- a/api_examples/glue.c
+++ b/api_examples/glue.c
@@ -60,13 +60,20 @@
 int api_search_sig(struct api_signature **sig) {
 
 	unsigned char *sp;
+	uint32_t search_start = 0;
+	uint32_t search_end = 0;
 
 	if (sig == NULL)
 		return 0;
 
-	sp = (unsigned char *)API_SEARCH_START;
+	if (search_hint == 0)
+		search_hint = 255 * 1024 * 1024;
+
+	search_start = search_hint & ~0x000fffff;
+	search_end = search_start + API_SEARCH_LEN - API_SIG_MAGLEN;
 
-	while ((sp + (int)API_SIG_MAGLEN) < (unsigned char *)API_SEARCH_END) {
+	sp = (unsigned char *)search_start;
+	while ((sp + API_SIG_MAGLEN) < (unsigned char *)search_end) {
 		if (!memcmp(sp, API_SIG_MAGIC, API_SIG_MAGLEN)) {
 			*sig = (struct api_signature *)sp;
 			if (valid_sig(*sig))