Allow the use of EEPROM_IN_RAM on MCUs.

If the MCU also supports PERSISTENT ram (not erased on a warm boot) it
allows testing of config changes without wearing out your flash.

e.g.

linker script
-------------
comment out __config_start/__config_end

target.c
--------
PERSISTENT uint8_t eepromData[EEPROM_SIZE]; // persistent, so it
survives warm boots.

target.h
--------
extern uint8_t eepromData[EEPROM_SIZE];

SITL actually keeps the EEPROM in a FILE, loaded into RAM using
alternate FLASH_* implementation.

src/test/unit/cli_unittest.cc

@@ -225,6 +225,10 @@ uint8_t getMotorCount() {
     return 4;
 }
 
+size_t getEEPROMStorageSize() {
+    return 0;
+}
+
 
 void setPrintfSerialPort(struct serialPort_s) {}