CI: Improve flow when building Linux artifacts

Move Linux artifact-related build commands into the artifact Makefile to
improve CI readability and simplify adding new Linux artifacts in the
future.

Author: ChinYikMing

.github/workflows/build-linux-artifacts.yml

@@ -55,11 +55,6 @@ jobs:
         run: |
           make build-linux-image
           make artifact ENABLE_PREBUILT=0 ENABLE_SYSTEM=1
-          mkdir -p /tmp/rv32emu-linux-image-prebuilt/linux-image
-          mv build/linux-image/Image /tmp/rv32emu-linux-image-prebuilt/linux-image
-          mv build/linux-image/rootfs.cpio /tmp/rv32emu-linux-image-prebuilt/linux-image
-          mv build/linux-image/simplefs.ko /tmp/rv32emu-linux-image-prebuilt/simplefs.ko
-          mv build/sha1sum-linux-image /tmp
       - name: Create tarball
         run: |
           cd /tmp

mk/artifact.mk

@@ -135,9 +135,14 @@ else
 endif
 else
 ifeq ($(call has, SYSTEM), 1)
+	$(Q)(mkdir -p /tmp/rv32emu-linux-image-prebuilt/linux-image)
 	$(Q)(cd $(BIN_DIR) && $(SHA1SUM) linux-image/Image >> sha1sum-linux-image)
 	$(Q)(cd $(BIN_DIR) && $(SHA1SUM) linux-image/rootfs.cpio >> sha1sum-linux-image)
 	$(Q)(cd $(BIN_DIR) && $(SHA1SUM) linux-image/simplefs.ko >> sha1sum-linux-image)
+	$(Q)(mv $(BIN_DIR)/sha1sum-linux-image /tmp)
+	$(Q)(mv $(BIN_DIR)/linux-image/Image /tmp/rv32emu-linux-image-prebuilt/linux-image)
+	$(Q)(mv $(BIN_DIR)/linux-image/rootfs.cpio /tmp/rv32emu-linux-image-prebuilt/linux-image)
+	$(Q)(mv $(BIN_DIR)/linux-image/simplefs.ko /tmp/rv32emu-linux-image-prebuilt/linux-image)
 else
 	git submodule update --init $(addprefix ./tests/,$(foreach tb,$(TEST_SUITES),$(tb)))
 	$(Q)for tb in $(TEST_SUITES); do \