EANY should disappear as a kind, and be replaced with ECALL and EBREAK.

[matthiasgoergens]

Risc0 uses an idiosyncratic decoding process. That forces them to introduce a new instruction kind, EANY that doesn't appear anywhere in the Risc-V spec. We inherited that limitation when we copy-and-pasted their code.

I suggest we remove EANY and replace it with ECALL and EBREAK, instructions that are actually mentioned in the spec.

EANY should disappear as a kind, and be replaced with ECALL and EBREAK.

EANY ain't even an instruction that appears in Risc-V. It's just an artifact of Risc0's design decisions.

(But we can do that in a subsequent PR.)

Originally posted by @matthiasgoergens in #538 (comment)