Fill empty UniformBufferBindingDescriptor only required

Fill empty UniformBufferBindingDescriptor only required

Until now, we try to reset 64 * 32 byte whenever we bind uniform buffers.
But usually we don't fully use 64 bindings for uniforms.

And also, NULL_DESCRIPTOTR could be replaced as memset(0), what we already doing
for standalone uniform buffer bindings.

To reduce those useless std::fill_n and memset,
let we call memset for binding only if we cannot assume the data will
be comes

Change-Id: I39ce8655da2f0aae96451f5d0c5025b98b25995a
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>