Legalize some more i8/i16 intructions (#524)

* Legalize some more i8/i16 intructions

cranelift/filetests/isa/x86/legalize-byte-ops-i8.clif

@@ -0,0 +1,36 @@
+test compile
+target x86_64
+
+; regex: V=v\d+
+
+function u0:0(i8, i8) fast {
+fn0 = %black_box(i8)
+ss0 = explicit_slot 1 ; black box
+
+ebb0(v0: i8, v1: i8):
+    v99 = stack_addr.i64 ss0
+
+    ; check: istore8 $(V), $(V)
+
+    v2 = band v0, v1
+    store v2, v99
+    v3 = bor v0, v1
+    store v3, v99
+    v4 = bxor v0, v1
+    store v4, v99
+    v5 = bnot v0
+    store v5, v99
+    v6 = band_not v0, v1
+    store v6, v99
+    v7 = bor_not v0, v1
+    store v7, v99
+    v8 = bxor_not v0, v1
+    store v8, v99
+    v9 = band_imm v0, 42
+    store v9, v99
+    v10 = bor_imm v0, 42
+    store v10, v99
+    v11 = bxor_imm v0, 42
+    store v11, v99
+    return
+}