Don't create copies of Icon bitmaps for Smartspace

We're serializing and transporting bitmaps as Icons via IPC. Right now,
this creates new copies when deserializing, which can create significant
increase in RSS+Anon memory usage in SysUI.

This change uses the same approach as Notification.java, where Icons are
stored in ashmem before being transported over IPC - this means we ever
only deserialize a buffer pointer.

Bug:287201133
Bug:275486055

Test: verified drop in RSS with perfetto on cheetah, cycling lockscreen
      200 times
Change-Id: I6b3a73732e3c49d04e28bdf1bf2e7c9638e61520