ACPI: EC: Replace atomic variables with bits

Number of flags is about to be increased, so it is better to
put them all into bits.
No functional changes.

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>