zram-swap: CONFIG_PROCD_ZRAM_TMPFS compatibility

Enable CONFIG_PROCD_ZRAM_TMPFS compatibility via two changes to list_cpu_idx():
* detect if /tmp is being used by /dev/zram0; if yes, offset initial value by 1 to skip first zram device.
* hot-add /dev/zram1, if not already present.

Signed-off-by: Conn O'Griofa <&gt;connogriofa@gmail.com>