target/i386: convert non-grouped, helper-based 2-byte opcodes

These have very simple generators and no need for complex group
decoding.  Apart from LAR/LSL which are simplified to use
gen_op_deposit_reg_v and movcond, the code is generally lifted
from translate.c into the generators.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>