[ELF] Please register ELF machine type for EraVM

[asl]

Consider officially registering EM_MACHINE enum value for EraVM. See https://www.sco.com/developers/gabi/latest/ch4.eheader.html for the (incomplete) list of current values.

This would required to correct mark ELF files with EraVM code inside.

In the meantime we will use and interim EM_ERAVM entry with value 260. Here is LLVM side of things: https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/BinaryFormat/ELF.h#L132