USB: dwc3-msm: Fix BC 1.2 compliance issues

BC1.2 spec requires PD to enable VDP_SRC when charging from DCP.
Hence, disallow PHY retention and collapse in order to supply VDP_SRC.
Also, address another issue seen during BC1.2 compliance testing when
using PHY based ASYNC IRQ where compliance device turns ON VBUS
immediately after turning it OFF. This may result in PD's failure to
ignore VBUS ON event sometimes.

Change-Id: I0e285afd93a910870c0461a66198002fa11bf68d
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>