Update riscv from 0.11.1 to 0.12.1

Summary: Updates riscv crate to latest version 0.12.1 and adjusts code to api changes within trap exception handling.

Reviewed By: jasonwhite

Differential Revision: D66851775

fbshipit-source-id: 2293d4692a8ad8cff9145d97a8309110dbafc882

Cargo.toml

@@ -14,7 +14,6 @@ perf-event-open-sys = { version = "4.0", git = "https://github.com/krallin/perf-
 plexi-core = { git = "https://github.com/haochenuw/plexi", rev = "a0326d9802a594ca5382b075620135607e1cdb23" }
 pyo3-build-config = { package = "pyo3-build-config", version = "0.21.2", git = "https://github.com/fbsource/pyo3", rev = "ff94a09031cc29d88d57ae3c846e5b871497aeb9" }
 quickcheck = { git = "https://github.com/jakoschiko/quickcheck", rev = "6ecdf5bb4b0132ce66670b4d46453aa022ea892c" }
-riscv = { git = "https://github.com/rust-embedded/riscv.git", rev = "28e9b02d45827055188be0dbd1f800ba64bc75e6" }
 tracing-attributes = { git = "https://github.com/tokio-rs/tracing.git", rev = "70a867877d5232b686d5fd70bbb4cbf37f4b38c6" }
 uefisettings = { git = "https://github.com/linuxboot/uefisettings", rev = "f16daed1d2bd1216204fd24e876c6477d03aebb3" }
 uefisettings_backend_thrift = { git = "https://github.com/linuxboot/uefisettings", rev = "f16daed1d2bd1216204fd24e876c6477d03aebb3" }