soc: qcom: smem: Zero out ramdump segment memory

The ramdump API uses fields other than those used by
the smem driver. Ensure that the ramdump segment structure
fields are zeroed out by using kcalloc instead of kmalloc_array.

Change-Id: I3e7139024d25d99e9fde89a54a18b131d418b1bc
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>