Vlv2TbltDevicePkg: assume GCC48 or later

Vlv2TbltDevicePkg: assume GCC48 or later

We're about to remove BaseTools support for GCC44..GCC47. Bump the
assumption about the minimum gcc version to GCC48 in
"Vlv2TbltDevicePkg/bld_vlv.sh".

No GCC44..GCC47 references remain under Vlv2TbltDevicePkg after this
patch.

Cc: Zailiang Sun <zailiang.sun@intel.com>
Cc: Yi Qian <yi.qian@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1377
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Zailiang Sun <zailiang.sun@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>