ACPI: Update the ACPI spec information in Kconfig

The UEFI Forum included the ACPI spec in its portfolio in October 2013
and will host future spec iterations, following the ACPI v5.0a release.

A UEFI Forum working group named ACPI Specification Working Group (ASWG)
has been established to handle future ACPI developments, any UEFI member
can join the group and contribute to ACPI specification.

So update the ownership and developers for ACPI in Kconfig accordingly,
and add another website link to ACPI specification too.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>