This patch fixes below build error by adding the missing asm/memory.h,
which is needed for arch_is_coherent().

$ make pxa3xx_defconfig; make
  CC      init/do_mounts_rd.o
In file included from include/linux/list_bl.h:5,
                 from include/linux/rculist_bl.h:7,
                 from include/linux/dcache.h:7,
                 from include/linux/fs.h:381,
                 from init/do_mounts_rd.c:3:
include/linux/bit_spinlock.h: In function 'bit_spin_unlock':
include/linux/bit_spinlock.h:61: error: implicit declaration of function 'arch_is_coherent'
make[1]: *** [init/do_mounts_rd.o] Error 1
make: *** [init] Error 2

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>