drm/etnaviv: Add command stream definitions required for a PPU flop reset

drm/etnaviv: Add command stream definitions required for a PPU flop reset

v2: move some defines that resided in etnaviv_flop_reset.c
    into the header as well

v3: fix spacing/tab stops

[cgmeiner: remove use of multiple blank lines]

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/20251119164624.9297-2-gert.wollny@collabora.com
Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>