esptool: Optimise generated image size by using RAM-loaded data for padding

Can save almost 128KB from some images.

components/esp32/ld/esp32.ld

@@ -37,7 +37,7 @@ MEMORY
                                      len = 0x50000 - CONFIG_TRACEMEM_RESERVE_DRAM - CONFIG_BT_RESERVE_DRAM
 
   /* Flash mapped constant data */
-  drom0_0_seg (R) :                  org = 0x3F400010, len = 0x800000
+  drom0_0_seg (R) :                  org = 0x3F400018, len = 0x800000
 
   /* RTC fast memory (executable). Persists over deep sleep.
    */

components/esptool_py/esptool

@@ -1 +1 @@
-Subproject commit ffde3f07b3ed735b6c9b9dfd0c12073a081444c1
+Subproject commit 325f01637b667af02cc6390965b09d50e6a31dac