Fix for the H747 flash driver / cache cleaning

This copies the approach of the STM32F7 flash driver submitted via
PR #10248

With this change the board finally passes all of the device key
tests 10/10 times correctly.

Author: Janne Kiiskila

targets/TARGET_STM/TARGET_STM32H7/flash_api.c

@@ -23,6 +23,7 @@
 
 static uint32_t GetSector(uint32_t Address);
 static uint32_t GetSectorSize(uint32_t Sector);
+static uint32_t GetSectorBase(uint32_t SectorId);
 
 int32_t flash_init(flash_t *obj)
 {
@@ -91,6 +92,9 @@ int32_t flash_erase_sector(flash_t *obj, uint32_t address)
         }
     }
 
+    SCB_CleanInvalidateDCache_by_Addr((uint32_t *)GetSectorBase(SectorId), GetSectorSize(SectorId));
+    SCB_InvalidateICache();
+
     HAL_FLASH_Lock();
 #if defined(DUAL_CORE)
     LL_HSEM_ReleaseLock(HSEM, CFG_HW_FLASH_SEMID, HSEM_CR_COREID_CURRENT);
@@ -103,6 +107,7 @@ int32_t flash_program_page(flash_t *obj, uint32_t address, const uint8_t *data,
 {
     uint32_t StartAddress = 0;
     int32_t status = 0;
+    uint32_t FullSize = size;
 
     if ((address >= (FLASH_BASE + FLASH_SIZE)) || (address < FLASH_BASE)) {
         return -1;
@@ -135,6 +140,9 @@ int32_t flash_program_page(flash_t *obj, uint32_t address, const uint8_t *data,
         }
     }
 
+    SCB_CleanInvalidateDCache_by_Addr((uint32_t *)StartAddress, FullSize);
+    SCB_InvalidateICache();
+
     HAL_FLASH_Lock();
 #if defined(DUAL_CORE)
     LL_HSEM_ReleaseLock(HSEM, CFG_HW_FLASH_SEMID, HSEM_CR_COREID_CURRENT);
@@ -213,6 +221,22 @@ static uint32_t GetSectorSize(uint32_t Sector)
     return (uint32_t)(128 * 1024); // 128 KB
 }
 
+/**
+  * @brief  Gets sector base address
+  * @param  SectorId
+  * @retval base address of a given sector
+  */
+static uint32_t GetSectorBase(uint32_t SectorId)
+{
+    uint32_t i = 0;
+    uint32_t address_sector = FLASH_BASE;
+
+    for (i = 0; i < SectorId; i++) {
+        address_sector += GetSectorSize(i);
+    }
+    return address_sector;
+}
+
 uint8_t flash_get_erase_value(const flash_t *obj)
 {
     (void)obj;