panfrost: Increase the maximum tiler heap size

Required to avoid tiler heap out-of-memory condition on Valhall on tests
including:

dEQP-GLES31.functional.draw_indirect.compute_interop.large.drawelements_combined_grid_1200x1200_drawcount_8

This test passes on Bifrost without the fix because varyings are only allocated
from the tiler heap on Valhall.

Minimal perf or memory usage impacted is expected, as even old versions of
panfrost.ko support growable memory.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <!16330>
47 jobs for !16330 with tiler-heap-size in 19 minutes and 27 seconds (queued for 4 seconds)
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