Shrink couple of x86 mterp handlers.

Use helpers to make more room for the follow-up CL.

Refactor the code so that it is possible to add
non-opcode specific helpers with custom name.

Test: test.py -b -r --interpreter -t 001-HelloWorld
Change-Id: I3714f83c10e1c16d3b26108e6eb475805482c785
8 files changed