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

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)
Cc: 3.13+ <stable@vger.kernel.org> # 3.13+
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>