drm/etnaviv: set up initial PULSE_EATER register

Set up the PULSE_EATER register (0x0010C) in etnaviv_gpu_hw_init. This
ports three mostly undocumented model/revision-specific register
overrides from the Vivante kernel driver.

This is relevant as at least the "disable internal DFS" for revisions >
0x5420 has shown to have a huge impact on shader performance (sped up
memory read performance by 7.5x and write performance by 1.5x) on an
affected GPU.

Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>