x86/APX: support JMPABS also in assembler

x86/APX: support JMPABS also in assembler

Without this APX support isn't really complete.

For Intel syntax displacement form is needed, such that symbolic
operands won't need prefixing by "offset". (The other form is actually
not used at all in Intel syntax.)

For the record: To restrict displacement form to Intel syntax is not
something I actually agree with.