cpu defs: uncomment empty extfeatures_ecx definition for Opteron_G1 (v2)

This should have no visible effect, but it should just clean up the
config file a bit.

This is based on a previous patch from John Cooper where this was introduced
with many other changes at the same time. Original John's patch submission is
at Message-ID: <4DDAD5E7.2020002@redhat.com>, <http://marc.info/?l=qemu-devel&m=130618871926030>.

Changes v1 -> v2:
 - Rebase against latest Qemu git tree
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

sysconfigs/target/target-x86_64.conf

@@ -66,7 +66,7 @@
    feature_edx = "sse2 sse fxsr mmx clflush pse36 pat cmov mca pge mtrr sep apic cx8 mce pae msr tsc pse de fpu"
    feature_ecx = "sse3"
    extfeature_edx = "lm fxsr mmx nx pse36 pat cmov mca pge mtrr syscall apic cx8 mce pae msr tsc pse de fpu"
-#   extfeature_ecx = ""
+   extfeature_ecx = " "
    xlevel = "0x80000008"
    model_id = "AMD Opteron 240 (Gen 1 Class Opteron)"