KVM: x86 emulator: simplify emulate_2op_SrcV()

emulate_2op_SrcV(), and its siblings, emulate_2op_SrcV_nobyte()
and emulate_2op_SrcB(), all use the same calling conventions
and all get passed exactly the same parameters.  Simplify them
by passing just the emulation context.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>