drm/i915/dg1: Drop final use of IS_DG1_GRAPHICS_STEP

All production DG1 hardware has graphics stepping B0; there is no such
thing as C0.  As such, we can simplify

        IS_DG1_GRAPHICS_STEP(uncore->i915, STEP_A0, STEP_C0)

to just match DG1 in general.

Bspec: 44463
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230127224313.4042331-4-matthew.d.roper@intel.com

drivers/gpu/drm/i915/gt/intel_region_lmem.c

@@ -158,7 +158,7 @@ static const struct intel_memory_region_ops intel_region_lmem_ops = {
 static bool get_legacy_lowmem_region(struct intel_uncore *uncore,
 				     u64 *start, u32 *size)
 {
-	if (!IS_DG1_GRAPHICS_STEP(uncore->i915, STEP_A0, STEP_C0))
+	if (!IS_DG1(uncore->i915))
 		return false;
 
 	*start = 0;

drivers/gpu/drm/i915/i915_drv.h

@@ -656,9 +656,6 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
 #define IS_RKL_DISPLAY_STEP(p, since, until) \
 	(IS_ROCKETLAKE(p) && IS_DISPLAY_STEP(p, since, until))
 
-#define IS_DG1_GRAPHICS_STEP(p, since, until) \
-	(IS_DG1(p) && IS_GRAPHICS_STEP(p, since, until))
-
 #define IS_ADLS_DISPLAY_STEP(__i915, since, until) \
 	(IS_ALDERLAKE_S(__i915) && \
 	 IS_DISPLAY_STEP(__i915, since, until))