USB: ci13xxx_msm: shutdown callback to disable D+ pullup

SW reset may not reset the PHY properly by disabling
the D+ pullup.

Implement a shutdown callback to disable the pullup
during soft reboot so that host controller does
not go in bad state.

Change-Id: I0923649f658b21f465a5391221db57863da43c08
Signed-off-by: Sujeet Kumar <ksujeet@codeaurora.org>