make eboot erase/read/write sector by sector

that makes possible having sketches with size up to the free size

bootloaders/eboot/flash.c

@@ -4,7 +4,7 @@
  * Redistribution and use is permitted according to the conditions of the
  * 3-clause BSD license to be found in the LICENSE file.
  */
- 
+/*
 #include <stddef.h>
 #include <stdint.h>
 #include <stdbool.h>
@@ -46,4 +46,4 @@ int SPIEraseAreaEx(const uint32_t start, const uint32_t size)
 
     return 0;
 }
-
+*/