drm/i915/gvt: better align the Makefile with i915 Makefile

Drop extra ccflags, drop extra intermediate variables, list object files
one per line alphabetically.

Cc: Zhi Wang <zhi.wang.linux@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/8bc0895376c077156a671e24ac6a5c75b7db4c9c.1649852517.git.jani.nikula@intel.comReviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

drivers/gpu/drm/i915/Makefile

@@ -320,10 +320,10 @@ i915-$(CONFIG_DRM_I915_SELFTEST) += \
 # virtual gpu code
 i915-y += i915_vgpu.o
 
-ifeq ($(CONFIG_DRM_I915_GVT),y)
-i915-y += intel_gvt.o intel_gvt_mmio_table.o
+i915-$(CONFIG_DRM_I915_GVT) += \
+	intel_gvt.o \
+	intel_gvt_mmio_table.o
 include $(src)/gvt/Makefile
-endif
 
 obj-$(CONFIG_DRM_I915) += i915.o
 obj-$(CONFIG_DRM_I915_GVT_KVMGT) += gvt/kvmgt.o

drivers/gpu/drm/i915/gvt/Makefile

 # SPDX-License-Identifier: GPL-2.0
-GVT_DIR := gvt
-GVT_SOURCE := gvt.o aperture_gm.o handlers.o vgpu.o trace_points.o firmware.o \
-	interrupt.o gtt.o cfg_space.o opregion.o mmio.o display.o edid.o \
-	execlist.o scheduler.o sched_policy.o mmio_context.o cmd_parser.o debugfs.o \
-	fb_decoder.o dmabuf.o page_track.o
 
-ccflags-y				+= -I $(srctree)/$(src) -I $(srctree)/$(src)/$(GVT_DIR)/
-i915-y					+= $(addprefix $(GVT_DIR)/, $(GVT_SOURCE))
+i915-$(CONFIG_DRM_I915_GVT) += \
+	gvt/aperture_gm.o \
+	gvt/cfg_space.o \
+	gvt/cmd_parser.o \
+	gvt/debugfs.o \
+	gvt/display.o \
+	gvt/dmabuf.o \
+	gvt/edid.o \
+	gvt/execlist.o \
+	gvt/fb_decoder.o \
+	gvt/firmware.o \
+	gvt/gtt.o \
+	gvt/gvt.o \
+	gvt/handlers.o \
+	gvt/interrupt.o \
+	gvt/mmio.o \
+	gvt/mmio_context.o \
+	gvt/opregion.o \
+	gvt/page_track.o \
+	gvt/sched_policy.o \
+	gvt/scheduler.o \
+	gvt/trace_points.o \
+	gvt/vgpu.o