QSPI: Move destructor into source file

This allows the entire QSPI class to be mocked/faked for unit testing
purpose, without dependencies from the real implementation such as
`qspi_free()` from the HAL.

Author: LDong-Arm

drivers/include/drivers/QSPI.h

@@ -115,12 +115,7 @@ class QSPI : private NonCopyable<QSPI> {
     QSPI(const qspi_pinmap_t &pinmap, int mode = 0);
     QSPI(const qspi_pinmap_t &&, int = 0) = delete; // prevent passing of temporary objects
 
-    virtual ~QSPI()
-    {
-        lock();
-        qspi_free(&_qspi);
-        unlock();
-    }
+    virtual ~QSPI();
 
     /** Configure the data transmission format
      *

drivers/source/QSPI.cpp

@@ -92,6 +92,13 @@ QSPI::QSPI(const qspi_pinmap_t &pinmap, int mode) : _qspi()
     MBED_ASSERT(success);
 }
 
+QSPI::~QSPI()
+{
+    lock();
+    qspi_free(&_qspi);
+    unlock();
+}
+
 qspi_status_t QSPI::configure_format(qspi_bus_width_t inst_width, qspi_bus_width_t address_width, qspi_address_size_t address_size, qspi_bus_width_t alt_width, qspi_alt_size_t alt_size, qspi_bus_width_t data_width, int dummy_cycles)
 {
     // Check that alt_size/alt_width are a valid combination