ENGR00272022 msl-mx6: usb: wait PHY clock stable explicitly

ENGR00272022 msl-mx6: usb: wait PHY clock stable explicitly

At mx6, if usb wakeup is not enabled, the PHY's power
will be off during the system suspend, so the dp/dm
will be unknown after the system resumes, it may wake up
controller at some boards since dp/dm's status satisfies
wake up condition. If the controller is waken up, the
PHCD will be cleared automatically.

According to IC requirement, after PHCD is cleared, we
need to wait 1ms before clear PHY's clock gate to wait
PHY's clock stable. At above condition, the PHCD is cleared
automatically, it may less than 1ms before we clear
PHY's clock gate, then, software operation to clear PHY's
clock gate will be useless. At this case, the PHY will works
abnormal, and cause the controller hang when we write some registers
(eg, portsc).

Signed-off-by: Peter Chen <peter.chen@freescale.com>