drm/msm/dp: fix AUX initialization sequence

Fix the AUX initialization sequence by resetting the AUX
hardware on every HPD-high, and powering down it down during
HPD-low. This ensures that the AUX hardware is ready to process
new requests triggered via both the USBPD callback and HPD
paths.

CRs-Fixed: 2105346
Change-Id: I394bedc5d39a78b8dbf59abf11789eaf6d823368
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>