Arm64: correct {su,us}dot SIMD encodings

Arm64: correct {su,us}dot SIMD encodings

According to the specification these permit the Q bit to control the
vector length operated on, and hence this bit should not already be set
in the opcode table entries (it rather needs setting dynamically). Note
how the test case output did also not match its input. Besides
correcting the test case also extend it to cover both forms.