Introduce instruction memory allocator

Necessary for dlfcn etc on ESP32, which has separate memory regions
for instruction and data.

known issues/todo
 * consider something similar to dual heaps for PROTOECTED
 * consider to adapt binfmt as well

boards/xtensa/esp32/esp32-core/scripts/esp32.template

@@ -60,3 +60,7 @@ MEMORY
 /* Heap ends at top of dram0_0_seg */
 
 _eheap = 0x40000000 - CONFIG_ESP32_TRACEMEM_RESERVE_DRAM;
+
+/* Module text area ends at top of dram0_0_seg */
+
+_emodtext = 0x400a0000;

boards/xtensa/esp32/esp32-core/scripts/esp32_flash.ld

@@ -59,6 +59,10 @@ SECTIONS
     *libpp.a:(.literal .text .literal.* .text.*)
     *libhal.a:(.literal .text .literal.* .text.*)
     _iram_text_end = ABSOLUTE(.);
+
+    /* Module text area starts at the end of iram0_0_seg */
+
+    _smodtext = ABSOLUTE(.);
   } > iram0_0_seg
 
   /* Shared RAM */

boards/xtensa/esp32/esp32-core/scripts/esp32_iram.ld

@@ -70,6 +70,9 @@ SECTIONS
     _text_end = ABSOLUTE(.);
     _etext = .;
 
+    /* Module text area starts at the end of iram0_0_seg */
+
+    _smodtext = ABSOLUTE(.);
   } > iram0_0_seg
 
   /* Shared RAM */