drm/etnaviv: Add support for running a PPU flop reset

[Gert Wollny]

Dear all, 

this is the second version of the patches to add a PPU flop reset to 
drm/etnaviv. The first version of the series was send as an RFC to
etnaviv at lists.freedesktop.org only.  

This series adds running the PPU flop reset which is required for some
hardware. This implementation was tested with the STM vendor kernel based on
linux-6.6.48 that is provided with
  https://github.com/STMicroelectronics/oe-manifest/
  Release: openstlinux-6.6-yocto-scarthgap-mpu-v25.04.30

The command stream is based on the stream that is emitted in the acccording
code of the galcore kernel. Since I have only a stm32mp257f-ev1 board t
test this for all parts that are emitted conditionally in the galcore kernel
only the part that is required for this board is submitted here.

Changes since v1 (RFC): 
 - clean up some code according to comments by Lucas,
 - move the ppu flop reset data into drm_private as suggested by Lucas
-  initialize flop reset data only once if any GPU needs it,
   For this is was also required to move the identification 
   of the hardware to etnaviv_gpu_bind,
 - move VIVS_ definitions out of etnaviv_flop_reset.c,
 - add a module parameter that makes it possible to force running the 
   PPU flop reset. 

Thanks for any comments,
Gert