fixed the following compile error when use avr32 atstk1006_defconfig:

  drivers/mtd/nand/atmel_nand.c: In function 'pmecc_err_location':
  drivers/mtd/nand/atmel_nand.c:639: error: implicit declaration of function 'writel_relaxed'

which was introduced by commit 1c7b874d ("mtd: at91: atmel_nand: add
Programmable Multibit ECC controller support").  The PMECC for nand
flash code uses writel_relaxed().  But in avr32, there is no macro
"writel_relaxed" defined.

This patch add writex_relaxed macro definitions.
Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Havard Skinnemoen <havard@skinnemoen.net>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>