Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC 264977:

Stop calling imx51_ccm_foo() clock functions from imx6 code. Instead
define a few imx_ccm_foo() functions that are implemented by the imx51
or imx6 ccm code.

MFC r261410

Follow r261352 by updating all drivers which are children of simplebus
to check the status property in their probe routines.

MFC r257383, r257384:

Add some bare-bones support for enabling usb and usbphy clocks.

Add a "no-op" USB PHY driver for imx-family SoCs.

Add a "no-op" USB PHY driver for imx-family SoCs. This is used when the
phy clocks need to be enabled, but no other hardware setup is needed to
make the phy work.