i.MX6: Set and clear the gating bits for Phase Fractional Dividers

This addresses silicon errata ERR006282 as described in this
document:
	https://community.freescale.com/docs/DOC-94581

Also implemented in Freescale's 2009.08-based release:

	http://git.freescale.com/git/cgit.cgi/imx/uboot-imx.git/


	Commit id: b7c5badf94ffbe6cd0845efbb75e16e05e3af404

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Stefano Babic <sbabic@denx.de>