broadcom/vc5: Update the UABI for in/out syncobjs

broadcom/vc5: Update the UABI for in/out syncobjs

This is the ABI I'm hoping to stabilize for merging the driver.  seqnos
are eliminated, which allows for the GPU scheduler to task-switch between
DRM fds even after submission to the kernel.  In/out sync objects are
introduced, to allow the Android fencing extension (not yet implemented,
but should be trivial), and to also allow the driver to tell the kernel to
not start a bin until a previous render is complete.