drm/i915: Fix __gen125_emit_bb_start() without WA

drm/i915: Fix __gen125_emit_bb_start() without WA

ce->wa_bb_page is allocated only for graphics version 12. However
__gen125_emit_bb_start() is used for any graphics version >= 12.50. For
the currently supported platforms this is not an issue, but for future
ones there's a mismatch causing the jump to
`wa_offset + DG2_PREDICATE_RESULT_BB` to be invalid since wa_offset is
not correct.

As in other places in the driver, check for graphics version "greater or
equal" to future-proof the support for new platforms.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220930050903.3479619-2-lucas.demarchi@intel.com