graphics: rework IComposer

Similar to IAllocator, introduce IComposerClient to manage resources.
Rework the interface such that most state changing calls are batched in a
"command buffer" and execute together.  The goal is to reduce the number
of IPC calls needed to set up the composer.

Test: builds and boots
Change-Id: I324009243234c4d2482ca0ef2591377b11530fc9