msm: kgsl: Allocate the VBO bind completion on the heap

The VBO bind operation is often synchronous, and needs to be waited
on by the ioctl thread. Allocate the completion struct used to synchronize
between the ioctl and bind operation on the heap for simplicity.

Change-Id: I709d417dbd3fb0ecd1150439f598fc3629de378e
Signed-off-by: Lynus Vaz <quic_lvaz@quicinc.com>