add signal handler code without any test just pass compile

Signed-off-by: Le Min <lemin9538@gmail.com>
modify the return value when fork

after fork the return vaule of father is > 0
and  0 is for child

Signed-off-by: Le Min <lemin9538@gmail.com>
release the file desc when release a process

Signed-off-by: Le Min <lemin9538@gmail.com>
add cpu_idle() function to system

Signed-off-by: Le Min <lemin9538@gmail.com>
add code to release the file desc when kill a process

Signed-off-by: Le Min <lemin9538@gmail.com>
enable signal process can call kill to send signal to others

Signed-off-by: Le Min <lemin9538@gmail.com>
fix a muxtex issue when get a new pid

Signed-off-by: Le Min <lemin9538@gmail.com>
enable the irq before suspend in case failded to get mutex

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