ACPI: tools: Exclude tools/* from .gitignore patterns

tools/power/acpi/.gitignore has the following entries:

  acpidbg
  acpidump
  ec

They are intended to ignore the following build artifacts:

  tools/power/acpi/acpidbg
  tools/power/acpi/acpidump
  tools/power/acpi/ec

However, those .gitignore entries are effective not only for the
current directory, but also for any sub-directories.

So, from the point of .gitignore grammar, the following check-in
directories are also considered to be ignored:

  tools/power/acpi/tools/acpidbg
  tools/power/acpi/tools/acpidump
  tools/power/acpi/tools/ec

As the manual gitignore(5) says "Files already tracked by Git are not
affected", this is not a problem as far as Git is concerned.

However, Git is not the only program that parses .gitignore because
.gitignore is useful to distinguish build artifacts from source files.

For example, tar(1) supports the --exclude-vcs-ignore option. As of
writing, this option does not work perfectly, but it intends to create
a tarball excluding files specified by .gitignore.

The issue can be prevented by prefixing the pattern with a slash; the
leading slash means the specified pattern is relative to the current
directory.

Do that for the "include" directory too for consistency and extra
safety.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>