utils: rename struct mem_region_t to struct mem_region

typedef mem_region_t mem_region_t;

... seems to work because they belong to different name-spaces,
but humans are confused even if compilers are not.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/lib/utils.h

@@ -19,7 +19,7 @@
 
 #include <types.h>
 
-typedef struct mem_region_t {
+typedef struct mem_region {
 	uintptr_t base;
 	size_t nbytes;
 } mem_region_t;