m68knommu: fix strace support for 68328/68360

strace enabled is marked using the `flags' field of the `thread_info' struct.
68360 version of entry.S did test a wrong bit in a wrong structure
(task_struct).

68328 version of entry.S did test the right bit in the right structure,
but wrongly, because the `flags' field is 32 bit wide, while the used
assembler insn (btst) only accesses a 8 bit byte in memory.

Fix both using code already used in the coldfire version of entry.S

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>