lm4: Add chip_read_reset_flags and chip_save_reset_flags
lm4: Add chip_read_reset_flags and chip_save_reset_flags

Battery backed up RAM is used to store the reset flags.

This patch wraps the code reading and writing the reset flags
with APIs for the consistency and make it available to external
callers like other chips.

Signed-off-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

BUG=chromium:1078470
BRANCH=none
TEST=buildall

Change-Id: I39c8646e57755d661b239979946df2871275878b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2182561
Reviewed-by: Craig Hesling <383db090fd8ef907a606ac8a9eccd2962bc489cf@chromium.org>
Commit-Queue: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Tested-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Auto-Submit: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec