devel/genromfs: Add new port

The mkfs equivalent for romfs filesystem. Port created for NuttX RTOS.
ROM FileSystem (ROMFS), read only filesystem, mainly for initial RAM
disks of installation disks. Using this filesystem, you get a very
similar feature, and even the possibility of a small kernel, with a
file system which doesn't take up useful memory from the router
functions in the basement of your office.

PR: 259242