Maintainers.txt: retitle "MdeModulePkg: ACPI S3 modules"

Maintainers.txt: retitle "MdeModulePkg: ACPI S3 modules"

The following two section titles in "Maintainers.txt" are not in
(case-sensitive) lexicographical order:

> MdeModulePkg: ACPI modules
> MdeModulePkg: ACPI S3 modules

However, if we simply sorted them, we'd have another problem: the specific
"ACPI S3 modules" line would precede the generic "ACPI modules" line.

Therefore, slightly reformulate the title on the second section, in order
to establish both lexicographical and hierarchical order.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2778
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200603160627.3594-2-lersek@redhat.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>