DDR UDQS and LDQS into one DQS controller
As I understand it...

UDQS = Upper byte data strobe (for upper 8 bits)

LDQS = Lower byte data strobe (for lower 8 bits)

So if your DDR3 controller has only one DQS then it only supports an 8-bit data bus. Therefore you can only use 8-bits of your DDR3 memory and must throw away the other 8-bits of bus width.

The chance of your processor only having an x8 DDR3 bus is rare, so I would double check your datasheet, footprint and whether the memory chip you have selected is ideal for this application.