In preparation of the next patch align with the datasheet (BSPEC
47112) with the naming of the pipe control set of flag values.
The variable "flags" in gen12_emit_flush_rcs() is applied as a
set of flags called Bit Group 1.

Define also the Bit Group 0 as bit_group_0 where currently only
PIPE_CONTROL0_HDC_PIPELINE_FLUSH bit is set.
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.8+
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230725001950.1014671-5-andi.shyti@linux.intel.com