coresight-tmc-etr: Use vmalloc once kcalloc fail

Sometimes system doesn't have enough continuous pages for kcalloc.
If kcalloc fail, use vmalloc instead.

Change-Id: Ie0864224f4eeedbd01b301f59b4eb307cc1f8df2
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>