refactor(measured boot): remove platform calls from Event Log driver

Currently, the Event Log driver does platform layer work by invoking
a few platform functions in the 'event_log_finalise' call. Doing
platform work does not seem to be the driver's responsibility, hence
moved 'event_log_finalise' function's implementation to the platform
layer.

Alongside, introduced few Event Log driver functions and done
some cosmetic changes.

Change-Id: I486160e17e5b0677c734fd202af7ccd85476a551
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
7 files changed