BaseTools: add handling for 'S:' flag to GetMaintainer.py

BaseTools: add handling for 'S:' flag to GetMaintainer.py

GetMaintainer.py already extracts the value of any S: tags for sections,
but it doesn't do anything with that information.

Print a warning message, with the status, for each matching section with
a status explicitly set to anything other than 'Supported' or
'Maintained'.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>