pwm: fix kernel crash using spinlock_t lock

pwm: fix kernel crash using spinlock_t lock

PD#148269: fix kernel panic when hibenating

1.Using mutex lock instead of spinlock_t lock.
2.Clk_prepare_enable might sleep could not use
  spinlock_t lock.
3.Add spinlock_t lock for clock_mux.
4.Panic message:
	BUG: sleeping function called from invalid context at
	kernel/locking/mutex.c:97
	in_atomic(): 1, irqs_disabled(): 128, pid: 2501, name: sh
	Preemption disabled at:[   69.935889@1] [<ffffff80097af728>]
	meson_pwm_apply+0x48/0x398

Change-Id: Ib2f42c4d757d1bb4bd8e4df0f90f7924be2fa799
Signed-off-by: Jian Hu <jian.hu@amlogic.com>