[CORE] scheduler: Use lite spin lock API in vmm_scheduler_state_change()

The usual spin lock APIs call vmm_scheduler_preempt_disable()/enable()
hence, we use lite spin lock API in vmm_scheduler_state_change() to avoid
state changes depending on preempt enable/disable and also make state
changes little faster.

Signed-off-by: Anup Patel <anup@brainfault.org>