ANDROID: logbuf: vendor hook for logbuf dump on oops

Initial kernel bootup logs get overwritten after running
for a long time, and there can be debugging scenario where
we need initial ~100s bootup logs for debugging.
'android_vh_initial_logbuf' vendor hook is helping in
achieving this purpose.

Bug: 185182649
Change-Id: I706824aeb566c09ecaf4b5900973d6cee8a2f35b
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>