fix(vfs/uart): add UART VFS select callback in IRAM

UART VFS select callback is placed in IRAM when CONFIG_UART_ISR_IN_IRAM is enabled

components/vfs/test_apps/pytest_vfs.py

@@ -11,7 +11,7 @@ from pytest_embedded import Dut
 @pytest.mark.esp32h2
 @pytest.mark.generic
 @pytest.mark.parametrize('config', [
-    'default',
+    'default', 'iram',
 ], indirect=True)
 def test_vfs_default(dut: Dut) -> None:
     dut.run_all_single_board_cases()