riscv: ptrace: cfi: expand "SS" references to "shadow stack" in uapi headers

riscv: ptrace: cfi: expand "SS" references to "shadow stack" in uapi headers

Similar to the recent change to expand "LP" to "branch landing pad",
let's expand "SS" in the ptrace uapi macros to "shadow stack" as well.
This aligns with the existing prctl() arguments, which use the
expanded "shadow stack" names, rather than just the abbreviation.

Link: https://lore.kernel.org/linux-riscv/CAHk-=whhSLGZAx3N5jJpb4GLFDqH_QvS07D+6BnkPWmCEzTAgw@mail.gmail.com/
Cc: Deepak Gupta <debug@rivosinc.com>
Signed-off-by: Paul Walmsley <pjw@kernel.org>