disp: msm: dp: init/deinit host only for cable connection/disconnection

DP host initialization and de-initialization need to be done only
in response to cable connect/disconnect events. De-initializing host
(which includes turning off all regulators), for every HPD low events
is unnecessary and can cause unintended issues with DP CTS tests.

CRs-Fixed: 2565704
Change-Id: I95ac71853dc14a46e4175cf0bee4c3eae315fc1e
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>