freedreno/a3xx/compiler: make IR heap dyanmic

freedreno/a3xx/compiler: make IR heap dyanmic

The fixed size heap is a remnant of the fdre-a3xx assembler.  Yet it is
convenient for being able to free the entire data structure in one shot
without worrying about leaking nodes.

Change it to dynamically grow the heap size (adding chunks) as needed so
we don't have an artificial upper limit on shader size (other than hw
limits) and don't always have to allocate worst-case size.

Signed-off-by: Rob Clark <robclark@freedesktop.org>