soc: qcom: boot_marker: Add provision to update marker

During recursive hibernation use case, if place_markers are used,
it results in duplication of entries. This patch adds provision to
update existing markers and if not present, create new entry. There
is a need to update bootloader boot stats during hibernation restore.
This is achieved by calling function update_bootloader_stats(). Make
this function local to boot_marker.c and use hibernation specific
markers to update boot stats. Also increase the BOOT_MARKER_MAX_LEN
to 50 chars to accommodate new entries.

Change-Id: I260be44519f013dbf626b92707f39de7d6ad7cdc
Signed-off-by: Arun KS <arunks@codeaurora.org>
Signed-off-by: Vivek Kumar <vivekuma@codeaurora.org>