feat: refactor and enhance documentation for Linux runtime, boot acceptance, and NPU integration

- Updated fault reference documentation to clarify Linux termination behavior and NPU-P6 requirements.
- Enhanced Linux runtime section with emphasis on platform setup and kernel handoff processes.
- Revised overview section to include detailed descriptions of NPU capabilities and memory configurations.
- Improved product use documentation to specify Linux rootfs behavior and acceptance checkpoints.
- Clarified reset summary to differentiate between Linux and smoke/NPU-P6 acceptance processes.
- Updated software section to reflect changes in Linux image loading and readiness protocols.
- Modified build scripts to support RV64 architecture and ensure proper ELF requirements.
- Enhanced NPU compiler to support cycle counting for RV64 and RV32 architectures.
- Added tests to validate new configurations and ensure compliance with updated publication contracts.

scripts/npu_compiler.py

@@ -261,7 +261,11 @@ static const rs_{prefix}_reloc_t rs_{prefix}_npu_relocations[{len(job.relocation
 {_c_bytes(f'rs_{prefix}_npu_params', job.params)}
 
 static uint64_t rs_{prefix}_cycles(void) {{
-#if defined(__riscv)
+#if defined(__riscv_xlen) && (__riscv_xlen == 64)
+    uint64_t cycle;
+    __asm__ volatile("rdcycle %0" : "=r"(cycle));
+    return cycle;
+#elif defined(__riscv)
     uint32_t high0; uint32_t low; uint32_t high1;
     do {{ __asm__ volatile("rdcycleh %0" : "=r"(high0));
          __asm__ volatile("rdcycle %0" : "=r"(low));