Fix Coverity issue: Initialize FlashIAP non-static member in constructor

drivers/FlashIAP.h

@@ -63,8 +63,10 @@ namespace mbed {
  */
 class FlashIAP : private NonCopyable<FlashIAP> {
 public:
-    FlashIAP();
-    ~FlashIAP();
+    constexpr FlashIAP() : _flash(), _page_buf(nullptr)
+    {
+
+    }
 
     /** Initialize a flash IAP device
      *

drivers/source/FlashIAP.cpp

@@ -46,16 +46,6 @@ static inline bool is_aligned(uint32_t number, uint32_t alignment)
     }
 }
 
-FlashIAP::FlashIAP() : _page_buf(nullptr)
-{
-
-}
-
-FlashIAP::~FlashIAP()
-{
-
-}
-
 int FlashIAP::init()
 {
     int ret = 0;

platform/NonCopyable.h

@@ -172,11 +172,11 @@ protected:
     /**
      * Disallow construction of NonCopyable objects from outside of its hierarchy.
      */
-    NonCopyable() { }
+    NonCopyable() = default;
     /**
      * Disallow destruction of NonCopyable objects from outside of its hierarchy.
      */
-    ~NonCopyable() { }
+    ~NonCopyable() = default;
 
 #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0))
     /**