USB: policy_engine: Enable VBUS after VCONN before PE_SRC_Startup

Currently driver is enabling VBUS first and then enable VCONN before
PE_SRC_startup when type C mode is POWER_SUPPLY_TYPEC_SINK_POWERED_CABLE.
On some platforms, enabling VBUS is taking time which is causing VCONN
reaching 2.7V after VBUS reaches VsafeV. This is exceeding 2msec timelimit
mentioned in type C specification and causes type C complaince tests
failure. Hence enable VCONN first and then enable VBUS to pass below
type C compliance tests:
TD 4.8.3 DRP Connect Vconn Accessory Test
TD 4.9.1 Source Suspend Test

Change-Id: I2697acdcaa063f251dd37035475392510037bee5
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>