USB: ehci-mxc: add work-around for efika mx/sb bug

Add support for setting CHRGVBUS to workaround a hardware bug on efika mx/sb
boards.
See http://lists.infradead.org/pipermail/linux-arm-kernel/2011-January/037341.html

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>