drm/i915/gt: Relocate Gen7 context-specific workarounds

CACHE_MODE_1 and CACHE_MODE_0 register should be saved and restored
as part of the context, not during engine reset. Move the related
workarounds (RC_OP_FLUSH_ENABLE, PIXEL_SUBSPAN_COLLECT_OPT_DISABLE)
from rcs_engine_wa_init() to gen7_ctx_workarounds_init() for
Gen7 platforms. This ensures the WA is applied during context
initialisation.

BSPEC: 11322, 11323

Signed-off-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/06cf152803ab0050e09c521ac2fc3637549860b3.1754902406.git.sebastian.brzezinka@intel.com