ACPI: Revert "ACPI / Battery: Remove battery's proc directory"

commit 3a670cc7 upstream.

The commit 1e2d9cdf and 7d7ee958 remove ACPI Proc Battery
directory and breaks some old userspace tools. This patch
is to revert commit 1e2d9cdf.

Fixes: 1e2d9cdf (ACPI / Battery: Remove battery's proc directory)
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>