soc: qcom: qdss_bridge: Get buffer num from mhi and enlarge buffer size

Update buffer number get from mhi device tree instead
of hardcode and modify buffer size as 32KB.

Change-Id: Ifca49161e8609a3cb1c06704e1fd778875b9bfca
Signed-off-by: Shaoqing Liu <shaoqingliu@codeaurora.org>