enable schecd() can work together with irq timer handle

Signed-off-by: Le Min <lemin9538@gmail.com>
add enter_critical and exit_critical to replace enable_irq and disable_irq

enter_critical will save the cpsr, this maily save the irq state
and disable irq. while exit_critical will restore the irq_state.

Signed-off-by: Le Min <lemin9538@gmail.com>
implement the basic function of mutex_lock and mutex_unlock

maybe there will be so many bugs, but we need time
next step, we need clean the code, and merge the menber
of task_sched to task_struct. ooh do not forget enable
a register dump of panic.

Signed-off-by: Le Min <lemin9538@gmail.com>