tests: gdbstub: minor refactor to the testcase.yaml

Change the `platform_allow` to multi-line format so that newly
supported archs/boards can be added as a new line.

Refactor the tags out to `common`, and add
`CONFIG_ARCH_HAS_GDBSTUB` filter

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>

tests/subsys/debug/gdbstub/testcase.yaml

@@ -4,10 +4,17 @@
 # SPDX-License-Identifier: Apache-2.0
 #
 
+common:
+  tags:
+    - debug
+    - gdbstub
+  filter: CONFIG_ARCH_HAS_GDBSTUB
+
 tests:
   # Connect to Zephyr gdbstub and run a simple GDB script
   debug.gdbstub.breakpoints:
-    platform_allow: qemu_x86
+    platform_allow:
+      - qemu_x86
     harness: pytest
     harness_config:
       pytest_root:
@@ -19,9 +26,6 @@ tests:
         - "test_breakpoints.gdbinit"
         - "--gdb_target_remote"
         - "tcp::5678"
-    tags:
-      - debug
-      - gdbstub
     extra_configs:
       # Make sure the gdbstub port chosen is unique for this test to avoid conflicts
       # when Twister runs tests in parallel on the same host.
@@ -33,7 +37,8 @@ tests:
   # Use non-default QEMU gdbstub port 1235 for this test to avoid conflicts
   # with some other test on QEMU running in parallel.
   debug.gdbstub_qemu.breakpoints:
-    platform_allow: qemu_x86
+    platform_allow:
+      - qemu_x86
     harness: pytest
     harness_config:
       pytest_root:
@@ -45,9 +50,6 @@ tests:
         - "test_breakpoints.gdbinit"
         - "--gdb_target_remote"
         - "tcp::1235"
-    tags:
-      - debug
-      - gdbstub
     extra_configs:
       # Turn off Zephyr's gdbstub for this test case.
       - CONFIG_GDBSTUB=n