avr32: add missing include causing undefined pgtable_page_* references

This patch adds the linux/mm.h header file to the AVR32 arch pgalloc.c
implementation to fix the undefined reference to pgtable_page_ctor() and
pgtable_page_dtor().
Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

arch/avr32/include/asm/pgalloc.h

@@ -8,6 +8,7 @@
 #ifndef __ASM_AVR32_PGALLOC_H
 #define __ASM_AVR32_PGALLOC_H
 
+#include <linux/mm.h>
 #include <linux/quicklist.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>