To support modification of OVMF NV storage, add an option "w" for
--ovmf to write the changed OVMF NV data section back to the OVMF image
from guest memory before deinit operations. This will enable persistent
EFI variables. Only option "w" is supported, dm will exit if passing
invalid option. It expects OVMF NV storage writeback with option "w"
when power off or reboot the UOS, poweroff, cold and warm reboot in EFI
shell and when dm recieves SIGINT and SIGHUP.
Tracked-On: #3413
Signed-off-by: Yang, Yu-chu <yu-chu.yang@intel.com>
Reviewed-by：Eddie Dong <eddie.dong@intel.com>
Acked-by: Yin Fengwei <fengwei.yin@intel.com>
16a7d2522c