target/sh4: Fix TB_FLAG_UNALIGN

The value previously chosen overlaps GUSA_MASK.

Rename all DELAY_SLOT_* and GUSA_* defines to emphasize
that they are included in TB_FLAGs.  Add aliases for the
FPSCR and SR bits that are included in TB_FLAGS, so that
we don't accidentally reassign those bits.

Fixes: 4da06fb3 ("target/sh4: Implement prctl_unalign_sigbus")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/856


Reviewed-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>