esp8266/boards: Move py/pairheap.c code from iRAM to iROM.

It doesn't need to be in iRAM.

Author: dpgeorge

ports/esp8266/boards/esp8266_common.ld

@@ -109,6 +109,7 @@ SECTIONS
         *py/nlr*.o*(.literal* .text*)
         *py/obj*.o*(.literal* .text*)
         *py/opmethods.o*(.literal* .text*)
+        *py/pairheap*.o*(.literal* .text*)
         *py/parse*.o*(.literal* .text*)
         *py/profile*.o*(.literal* .text*)
         *py/qstr.o*(.literal* .text*)