vm/interp: Code cleanups

Signed-off-by: Pekka Enberg <penberg@kernel.org>
vm/interp: Add 'frame' data structure for interpreter

Signed-off-by: Pekka Enberg <penberg@kernel.org>
vm/interp: Push method arguments on operand stack

Signed-off-by: Pekka Enberg <penberg@kernel.org>
vm/interp: Make interpret() structure similar to BC2IR

Make the interpret() function structure look similar to what we have in
the BC2IR code in LLVM backend.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
vm/interp: Add interpreter for OPC_GETSTATIC

Signed-off-by: Pekka Enberg <penberg@kernel.org>