target-sh4: move intr_at_halt out of cpu_halted()

target-sh4: move intr_at_halt out of cpu_halted()

All targets except SH4 have the same cpu_halted() routine, and it has
only one caller. It is therefore a good candidate for inlining.

The difference is the handling of the intr_at_halt, which is necessary
to ignore SR.BL when sleeping. Move intr_at_halt handling out of it, by
setting this variable while executing the sleep instruction, and
clearing it when the CPU has been woken-up by an interrupt, whatever the
state of SR.BL. Also rename this variable in_sleep.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>