soc: qcom: Increase bootmarker read buffer

There are more users to bootmarker now. Increase bootmarker
read buffer to accommodate for all. Add checks to catch buffer
overflow.

Change-Id: Icc7db4c041d72008b5090685da0db0da7a155efb
Signed-off-by: Shreyas K K <shrekk@codeaurora.org>