elog: Use the RTC driver interface instead of reading CMOS directly.

elog: Use the RTC driver interface instead of reading CMOS directly.

Use the RTC driver interface to find the timestamp for events instead of
reading the CMOS based RTC directly on x86 or punting on ARM. This makes
timestamps available on both architectures, assuming an RTC driver is
available.

BUG=None
TEST=Built and booted on nyan_big and link and verified that the timestamps
in the event log were accurate.
BRANCH=nyan

Original-Change-Id: Id45da53bc7ddfac8dd0978e7f2a3b8bc2c7ea753
Original-Signed-off-by: Gabe Black <gabeblack@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/197798
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Original-Tested-by: Gabe Black <gabeblack@chromium.org>
Original-Commit-Queue: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 493b05e06dd461532c9366fb09025efb3568a975)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Change-Id: I4fad296ecfeff8987e4a18054661190239245f32
Reviewed-on: http://review.coreboot.org/7891
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>