NVRAM refactor, phase 1. (#18969)

* Rename `eeprom_stm32` to `eeprom_legacy_emulated_flash`.

* Rename `flash_stm32` to `legacy_flash_ops`.

* Rename `eeprom_teensy` to `eeprom_kinetis_flexram`.

platforms/chibios/drivers/flash/legacy_flash_ops.c

@@ -17,7 +17,7 @@
  */
 
 #include <hal.h>
-#include "flash_stm32.h"
+#include "legacy_flash_ops.h"
 
 #if defined(STM32F1XX)
 #    define FLASH_SR_WRPERR FLASH_SR_WRPRTERR

platforms/chibios/drivers/flash/legacy_flash_ops.h

@@ -24,7 +24,7 @@ extern "C" {
 
 #include <stdint.h>
 
-#ifdef FLASH_STM32_MOCKED
+#ifdef LEGACY_FLASH_OPS_MOCKED
 extern uint8_t FlashBuf[MOCK_FLASH_SIZE];
 #endif