ACPI / EC: Clean up EC GPE mask flag

EC_FLAGS_COMMAND_STORM is actually used to mask GPE during IRQ processing.
This patch cleans it up using more readable flag/function names.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Tested-by: Tomislav Ivek <tomislav.ivek@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>