Ext4Pkg: Add handling of EFI_FILE_SYSTEM_VOLUME_LABEL GetInfo().

This commit adds support for EFI_FILE_SYSTEM_VOLUME_LABEL requests
in GetInfo().

Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>