drm/etnaviv: Add module parameter to force PPU flop reset

drm/etnaviv: Add module parameter to force PPU flop reset

v2: Check for feature PIPE_3D when forcing PPU flop reset (Lucas)

v3: - drop use of ppu_flop_reset enum (Christian Gmeiner)
    - don't initialize module parameter to zero (checkpatch)
    - avoid multi-line string in warning message (checkpatch)

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Tested-by: Marek Vasut <marek.vasut@mailbox.org> # STM32MP255C DHCOS DHSBC
Link: https://patch.msgid.link/20251119164624.9297-6-gert.wollny@collabora.com
Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>