dataplacement: update ruh info initialization

dataplacement: update ruh info initialization

The current way of initilization limits ruhs to 128. This commit
updates the way we fetch ruhs. We now fetch the ruhs info in two steps.
The first step only gets us the number of ruhs from the ioengine. This
is used by fdp backend to allocate the correct buffer size for the
second step, where we fetch the actual ruhs info. Fio no longer limits
the maximum number of ruhs for a device.

Signed-off-by: Ankit Kumar <ankit.kumar@samsung.com>
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
[Vincent: edited commit message]