aarch64: enlarge value buffer of arm_reg to store 64 bit

struct arm_reg::value[] must be 8 byte to hold a 64bit register value.

Change-Id: If253e90731d0ee855eafd9d7b63b91f84630cc7c
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>

src/target/armv8.c

@@ -1168,7 +1168,7 @@ struct reg_cache *armv8_build_reg_cache(struct target *target)
 
 		reg_list[i].name = armv8_regs[i].name;
 		reg_list[i].size = armv8_regs[i].bits;
-		reg_list[i].value = calloc(1, 8);
+		reg_list[i].value = &arch_info[i].value[0];
 		reg_list[i].type = &armv8_reg_type;
 		reg_list[i].arch_info = &arch_info[i];