qpnp-smb2: implement PE_START property

The policy engine needs to be informed that its time to start
its activities when APSD results are available and/or PD_ALLOWED
is decided. USB type property shouldn't change after that.

Since HVDCP_TIMEOUT_VOTER is the last one to cast its allow vote
in the sequence, use it to reflect the PE_START property.

While at it since PE_START property is returned assuming an atomic
context, the read of PD_ALLOWED could be moved to its sleepable
variants. This aids in keeping the policy engine code simple and also
assures race free code.

Change-Id: Ib98ac10d87200a2fd5492e27399f696f2468eba6
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>