esp32: Provision to redirect .bss to external ram through linker fragments

Include external ram section in the linker template to process it
through linker script generation mechanism. This enables redirection of .bss section to external memory using linker fragments

libnet80211, libpp, libbt, liblwip: Redirect .bss through fragments

components/esp32/ld/esp32.project.ld.in

@@ -232,12 +232,22 @@ SECTIONS
     _noinit_end = ABSOLUTE(.);
   } > dram0_0_seg
 
+   /* external memory bss, from any global variable with EXT_RAM_ATTR attribute*/
+  .ext_ram.bss (NOLOAD) :
+  {
+    _ext_ram_bss_start = ABSOLUTE(.);
+
+    mapping[extern_ram]
+
+    . = ALIGN(4);
+    _ext_ram_bss_end = ABSOLUTE(.);
+  } > extern_ram_seg
+
   /* Shared RAM */
   .dram0.bss (NOLOAD) :
   {
     . = ALIGN (8);
     _bss_start = ABSOLUTE(.);
-    *(.ext_ram.bss*)
     _bt_bss_start = ABSOLUTE(.);
     *libbt.a:(.bss .bss.* COMMON)
     . = ALIGN (4);
@@ -253,18 +263,6 @@ SECTIONS
 
     mapping[dram0_bss]
 
-    *(.dynsbss)
-    *(.sbss)
-    *(.sbss.*)
-    *(.gnu.linkonce.sb.*)
-    *(.scommon)
-    *(.sbss2)
-    *(.sbss2.*)
-    *(.gnu.linkonce.sb2.*)
-    *(.dynbss)
-    *(.share.mem)
-    *(.gnu.linkonce.b.*)
-
     . = ALIGN (8);
     _bss_end = ABSOLUTE(.);
   } > dram0_0_seg