Implement uc_reg_{read,write}{,_batch}2 APIs.

These APIs take size parameters, which can be used to properly bounds-check the
inputs and outputs for various registers. Additionally, all backends now throw
UC_ERR_ARG if the input register numbers are invalid.

Completes #1831.

qemu/unicorn_common.h

@@ -128,4 +128,15 @@ static inline void uc_common_init(struct uc_struct* uc)
     if (!uc->release)
         uc->release = release_common;
 }
+
+#define CHECK_REG_TYPE(type) do {    \
+    if (size) {                      \
+        if (*size < sizeof(type)) {  \
+            return UC_ERR_NOMEM;     \
+        }                            \
+        *size = sizeof(type);        \
+    }                                \
+    ret = UC_ERR_OK;                 \
+} while(0)
+
 #endif