ACPICA: Events: Split acpi_ev_associate_reg_method() from region initialization code

ACPICA commit 87c85610250ff7141a84507f68dbc1e00f2936db

This patch introduces a new region initialization function
acpi_ev_associate_reg_method(), which is invoked to associate the _REG method
to its related region object.

Region object's default value assignments are also sorted by cleaning up
the code using this new function. Lv Zheng.

Link: https://github.com/acpica/acpica/commit/87c85610


Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>