Add riscv64 build support (#7309)

Lighthouse does not compile on the _riscv64_ architecture due to a missing target configuration in the `bls_hardware_acceleration` function.


  Added support for compiling Lighthouse on the riscv64 architecture by explicitly handling the _riscv64_ target in the bls_hardware_acceleration function.
Specifically, this line was added:
```
#[cfg(target_arch = "riscv64")]
return false;
```
This prevents a compilation error on RISC-V.

lighthouse/src/main.rs

@@ -68,6 +68,9 @@ fn bls_hardware_acceleration() -> bool {
 
     #[cfg(target_arch = "aarch64")]
     return std::arch::is_aarch64_feature_detected!("neon");
+
+    #[cfg(target_arch = "riscv64")]
+    return false;
 }
 
 fn allocator_name() -> String {