Replace srec_cat with objcopy

We currently use srec_cat from srecord to create vmem files. objcopy does have similar functionality, but https://sourceware.org/bugzilla/show_bug.cgi?id=19921 was needed first. That patch landed, and binutils 2.33 should be the first release with a fixed objcopy. Once our toolchain has that version of binutils, try it and remove the srecord dependency.

Start by locating the current srec_cat invocation and the toolchain version configuration. Verify that the available binutils objcopy supports the required VMEM conversion, then run the existing VMEM-generation flow. Done means objcopy produces equivalent files and the srecord dependency can be removed.

Written by the indexing model from the issue text.