s390x/tcg: Implement SUBTRACT HALFWORD (SGH)

Easy to wire up.

Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200928122717.30586-4-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

target/s390x/insn-data.def

@@ -886,6 +886,7 @@
 /* SUBTRACT HALFWORD */
     C(0x4b00, SH,      RX_a,  Z,   r1, m2_16s, new, r1_32, sub, subs32)
     C(0xe37b, SHY,     RXY_a, LD,  r1, m2_16s, new, r1_32, sub, subs32)
+    C(0xe339, SGH,     RXY_a, MIE2,r1, m2_16s, r1, 0, sub, subs64)
 /* SUBTRACT HIGH */
     C(0xb9c9, SHHHR,   RRF_a, HW,  r2_sr32, r3_sr32, new, r1_32h, sub, subs32)
     C(0xb9d9, SHHLR,   RRF_a, HW,  r2_sr32, r3, new, r1_32h, sub, subs32)