This change affects arm, arm64 and mips achitectures.
Additonally, it removes redundant checks for kdb_active where it
already results in kdb_reenter() and adds kdb_reenter() calls
where they were missing.
Some architectures check the return value of kdb_trap(), but some don't.
I haven't changed any of that.
Some trap handling routines have a return code.
I am not sure if I provided correct ones for returns after kdb_reenter().
It should not return unless kdb_jmpbufp is NULL for some reason.