Support for Microchip PolarFire SoC (MPFS250)

[dgarske]

Summary

This PR adds full support for the Microchip PolarFire SoC (MPFS250T) secure boot target, along with a refactoring of GPT (GUID Partition Table) code to make it reusable across multiple architectures.

Key Changes

1. New Platform: Microchip PolarFire SoC (MPFS250)

• Architecture: RISC-V 64-bit (rv64imac) with five-core CPU cluster (1× E51 monitor core + 4× U54 application cores)
• New HAL files:
  • hal/mpfs250.c - Hardware abstraction layer implementation (UART and uSD)
  • hal/mpfs250.h - Register definitions and hardware interfaces
  • hal/mpfs250.ld - Linker script for the platform
  • hal/mpfs.dts / hal/mpfs.dtb - Device tree source and binary
  • hal/mpfs.yaml - HSS payload generator configuration
• New boot files:
  • src/boot_riscv64.c - RISC-V 64-bit boot logic
  • src/boot_riscv64_start.S - Assembly startup code
  • src/vector_riscv64.S - Interrupt vector table
• Test application: test-app/app_mpfs250.c with linker script
• Example configuration: config/examples/polarfire_mpfs250.config

2. GPT Refactoring for Cross-Platform Use

Refactored the x86-specific GPT code into a generic, reusable implementation:

• New generic GPT module: src/gpt.c + include/gpt.h - Platform-independent GPT parsing
• Disk abstraction: include/disk.h - Common disk interface definitions
• Renamed: src/x86/gpt.c → src/x86/disk.c (now contains x86-specific disk operations)
• Enhanced update_disk.c: Updated to work with the generic GPT interface for non-x86 targets

3. Build & CI Updates

• Added MPFS250 to test-configs.yml workflow for automated build testing
• Updated arch.mk with RISCV64 architecture support and MPFS250 target rules
• Tool Makefile updates for cross-compilation compatibility

Testing

• Build tested with example configuration
• Added to CI build test matrix

Documentation

Added comprehensive documentation in docs/Targets.md covering:

• Feature overview
• Build instructions
• HSS payload generation
• Flashing procedures (eMMC/SD via USB-DMSC, eNVM)
• OpenOCD debugging setup

Future Work (documented)

1. Full HSS replacement support using wolfBoot
2. eMMC and QSPI NOR flash driver implementations