drivers/staging/zram: backport zram from 3.7 kernel

All commits up to:
  zram: Fix deadlock bug in partial read/write

Signed-off-by: Willi Ye <williye97@gmail.com>

Conflicts:
	drivers/staging/zram/Kconfig
	drivers/staging/zram/zram_drv.c

Conflicts:
	drivers/staging/zram/Kconfig
	drivers/staging/zram/zram_drv.c