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: I304cbf01e6d5b5a55848d4aa8775eecd95293bb3
Signed-off-by: Shaoqing Liu <shaoqingliu@codeaurora.org>