Add default maxBufferCount in GraphicBufferProducer

Some modules that inherit and use IGraphicBufferProducer
don't set maxBufferCount. As a result, the maxBufferCount value
that has been queried in libvulkan is 0,
and the creation of swapchain fails.

Therefore, the default value (64) is set to maxBufferCount.

Test: build, Mcts
Bug: 376142095

Change-Id: Ie5c5f747ecd6c15ffae80cc32b9f5a90b1a44df3
Signed-off-by: sm1021.shin <sm1021.shin@samsung.com>