partitions: increase MAX_SEARCH_PARTITIONS and move to part.h

Move MAX_SEARCH_PARTITIONS to part.h so that functions in cmd
directory can find it.  At the same time, increase the value to
64 since some operating systems use many, and the resources
consumed by a larger value are minimal.

Changes since v6: none.

Signed-off-by: Alison Chaiken <alison@peloton-tech.com>
diff --git a/include/part.h b/include/part.h
index 87b1111..22da604 100644
--- a/include/part.h
+++ b/include/part.h
@@ -49,6 +49,7 @@
 
 #define PART_NAME_LEN 32
 #define PART_TYPE_LEN 32
+#define MAX_SEARCH_PARTITIONS 64
 
 typedef struct disk_partition {
 	lbaint_t	start;	/* # of first block in partition	*/