MLK-9606-2 usb: otg: test: start tst_maint timer and set otg_vbus_off flag

MLK-9606-2 usb: otg: test: start tst_maint timer and set otg_vbus_off flag

This patch adds 2 variables: tst_maint and otg_vbus_off, tst_maint is to check if
current session for test device; otg_vbus_off is to notify if A device need turn
off vbus immediately after B device disconnects.
The otg test device handling is added into ehset driver, for that device,
A-device should start a timer for maintain the session, and set otg_vbus_off
flag according to its bcdDevice value.

Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Li Jun <b47624@freescale.com>
(cherry picked from commit 78a2c14bdea4b8e334c7e0afad074b61b71193cb)
(cherry picked from commit b854141cc5a7150751e7f7fd2dfb10a415cfea10)