util: add generic block device listener helper

Various of our tools operate on block devices, and it's not always
obvious to know which block devices are actually appropriate for use.
Hence, let's add a helper that allows to list block devices, and
supports some limited filtering.

src/shared/blockdev-list.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+typedef enum BlockDevListFlags {
+        BLOCKDEV_LIST_SHOW_SYMLINKS              = 1 << 0,
+        BLOCKDEV_LIST_REQUIRE_PARTITION_SCANNING = 1 << 1,
+        BLOCKDEV_LIST_IGNORE_ZRAM                = 1 << 2,
+        BLOCKDEV_LIST_REQUIRE_LUKS               = 1 << 3,
+} BlockDevListFlags;
+
+int blockdev_list(BlockDevListFlags flags);