tools/power/acpi: Add .gitignore file

Add a .gitignore file so that git commands do not pick up the resulting
binaries and directories.
Signed-off-by: NPrarit Bhargava <prarit@redhat.com>
Acked-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

tools/power/acpi/.gitignore

+acpidbg
+acpidump
+ec
+include