x11-wm/dwm: Add option to enable volume control keys [0]

• Assign to 0mp [1]. The current maintainer hasn't responded to PRs since 2012.
• While here rename SUPERASMODKEY patch for consistency with the new volume keys patch
• Fix variable order

PR: 226924 [0], 226929 [1]
Submitted by: Ashish Gupta <ashmew2@gmail.com> [0], 0mp [1]
Approved by: maintainer timeouts