cpu/esp32x: generate section.ld from section.ld.in

Using `sectoins.ld.in` instead of a static `sections.ld`, from which the actual used `sections.ld` is generated with the C preprocessor, allows to use the configuration in `sdkconfig.h` as well as Kconfig to use a custom section layout.

cpu/esp32/ld/esp32/sections.ld.in

@@ -18,6 +18,7 @@ SECTIONS
   .rtc.text :
   {
     . = ALIGN(4);
+    _rtc_text_start = ABSOLUTE(.);
 
     *(.rtc.literal .rtc.text .rtc.text.*)
 
@@ -452,6 +453,19 @@ SECTIONS
   . = 0x40000000;
   _eheap3 = ABSOLUTE(.);
 
+  .flash.appdesc : ALIGN(0x10)
+  {
+    _rodata_start = ABSOLUTE(.);
+
+    *(.rodata_desc .rodata_desc.*)               /* Should be the first.  App version info.        DO NOT PUT ANYTHING BEFORE IT! */
+    *(.rodata_custom_desc .rodata_custom_desc.*) /* Should be the second. Custom app version info. DO NOT PUT ANYTHING BEFORE IT! */
+
+    /* Create an empty gap within this section. Thanks to this, the end of this
+     * section will match .flah.rodata's begin address. Thus, both sections
+     * will be merged when creating the final bin image. */
+    . = ALIGN(ALIGNOF(.flash.rodata));
+  } >default_rodata_seg
+
   _rodata_start = ABSOLUTE(.);
   .flash.rodata : ALIGN(0x10)
   {