target-mips: Use cpu_exec_interrupt qom hook

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-microblaze: Use cpu_exec_interrupt qom hook

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-lm32: Use cpu_exec_interrupt qom hook

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-ppc: Use cpu_exec_interrupt qom hook

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-i386: Use cpu_exec_interrupt qom hook

Signed-off-by: Richard Henderson <rth@twiddle.net>
cpu-exec: Do CPU_INTERRUPT_HALT unconditionally

The signal is currently checked by 10 targets, but only actually
raised by Sparc and ARM.  For the sake of one test-and-branch,
we can handle this generic bit generically.

Signed-off-by: Richard Henderson <rth@twiddle.net>