target/m68k: implement m68k "any instruction" trace mode

target/m68k: implement m68k "any instruction" trace mode

The m68k trace mode is controlled by the top 2 bits in the SR register. Implement
the m68k "any instruction" trace mode where bit T1=1 and bit T0=0 in which the CPU
generates an EXCP_TRACE exception (vector 9 or offset 0x24) after executing each
instruction.

This functionality is used by the NetBSD kernel debugger to allow single-stepping
on m68k architectures.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210519142917.16693-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>