staging: android: persistent_ram: Introduce persistent_ram_new()

The routine just creates a persistent ram zone at a specified address.

For persistent_ram_init_ringbuffer() we'd need to add a
'struct persistent_ram' to the global list, and associate it with a
device. We don't need all this complexity in pstore_ram, so we introduce
the simple function.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>