Proposal: Add dependency to Zicsr

[a4lg]

This is the same series of proposals (add dependency to Zicsr from unprivileged extensions with CSR):

• Zcmt → Zicsr dependency? riscvarchive/riscv-code-size-reduction#179 (Resolved)
• Zjpm Proposal: Add dependency to Zicsr riscv-j-extension#17 (Resolved)
• Proposal: Add dependency to Zicsr riscv-p-spec#145 (open but will be reflected)

Although Zisslpcfi has privileged part (all privileged extensions have indirect dependency to Zicsr through the privileged architecture), this extension contains user-accessible CSRs. So, adding Zicsr to the dependency would be nice and clearer (for toolchains implementing this Zisslpcfi extension).

[ved-rivos]

Agree. Added by PR #15