third-party/rust: bring in PRs for riscv

Summary:
Bring in:
- rust-embedded/riscv#206 - Eq for Permission
- rust-embedded/riscv#207 - Mstatus update operations

Details of 207 are still under discussion so this will probably need another freshen (and go back to pulling from the riscv repo once its landed).

Reviewed By: dtolnay

Differential Revision: D57136236

fbshipit-source-id: 09e5365d3fd499c4dccae7d2ada333bf369fac47

Cargo.toml

@@ -12,7 +12,7 @@ pcics = { git = "https://github.com/peterdelevoryas/pcics.git", rev = "aac7ac4b9
 perf-event = { version = "0.4", git = "https://github.com/krallin/perf-event.git", rev = "86224a9bc025d5d19f719542f27c8c629a08b167" }
 perf-event-open-sys = { version = "4.0", git = "https://github.com/krallin/perf-event.git", rev = "86224a9bc025d5d19f719542f27c8c629a08b167" }
 quickcheck = { git = "https://github.com/jakoschiko/quickcheck", rev = "6ecdf5bb4b0132ce66670b4d46453aa022ea892c" }
-riscv = { git = "https://github.com/rust-embedded/riscv.git", rev = "288d02328b4bc2ac966ba3dda5c5032e8a712dff" }
+riscv = { git = "https://github.com/jsgf/riscv.git", rev = "a2a988817419b4617a5cb4dbefdf4f0fded0ac49" }
 
 [workspace]
 members = [