Support scan plan attribute for scheduled scan

Support scan plan attribute for scheduled scan

This adds the support of the scan plan attribute.
With kernel updates, driver can no longer diffrentiate interval
attribute from single scan plan attribute, so driver's pno scan
back off logic cannot be triggered in that case.
To solve the PNO back-off problem, this CL allows wificond to explicitly
specify scan plans (if the driver supports it). With explicit scan
plans, the driver will have the information it needs to back-off PNO
scans.

Bug: 63837760
Test: compile, unit tests
Test: Manually test that pno scan works on multiple devices
Test: Integration sanity test

Change-Id: Ic7e38caa482a2d72f45bf3c8177fa656e534db08