tcg: Introduce TCG_COND_TST{EQ,NE}
target/alpha: Use TCG_COND_TST{EQ,NE}
target/m68k: Use TCG_COND_TST{EQ,NE} in gen_fcc_cond
target/sparc: Use TCG_COND_TSTEQ in gen_op_mulscc
target/s390x: Use TCG_COND_TSTNE for CC_OP_{TM,ICM}
target/s390x: Improve general case of disas_jcc