ENGR00232583 Mx6 USB host: Set HCD_FLAG_HW_ACCESSIBLE flag after clock gate

ENGR00232583 Mx6 USB host: Set HCD_FLAG_HW_ACCESSIBLE flag after clock gate

There is a USB hang issue when do system suspend/resume test with a USB
device plug in. The issue is caused by USB host driver accessing register
when clock is off. Currently set HCD_FLAG_HW_ACCESSIBLE bit before open
clock in ehci_fsl_bus_resume, it cause accessing register without clock.
So we should change the code call order to avoid driver access register
without clock.

- Set HCD_FLAG_HW_ACCESSIBLE software flag after HW clock turn on
- remove some unnecessary code in ehci_fsl_pre_irq

Signed-off-by: make shi <b15407@freescale.com>