Add MPFS250 QSPI support

[dgarske]

Summary

• Add MPFS250 QSPI support with two access paths: direct MSS QSPI controller and System Controller SPI services.
• Introduce a QSPI-focused PolarFire config and extend the HAL/external-flash APIs for QSPI read/write/erase and SCB mailbox reads.
• Tweak RISC-V build flow to select update loader based on disk usage and sign ELF outputs when ELF mode is enabled.
• Add a PolarFire programming helper script and document QSPI usage under PolarFire targets.

Key Changes

• New example config: config/examples/polarfire_mpfs250_qspi.config
• QSPI init + drivers in hal/mpfs250.c (MSS QSPI + SC SPI paths)
• Build logic updates in arch.mk for update loader selection + ELF signing
• PolarFire QSPI documentation in docs/Targets.md
• New tooling script: tools/scripts/mpfs_program.sh

Testing

• Example output (with DEBUG_QSPI set):

wolfBoot Version: 2.7.0 (Jan 29 2026 13:03:10)
QSPI: Using System Controller SPI services
SC SPI: Read 0x20000 -> 0x80013680, len 512
SC SPI: Read 0x2000000 -> 0x80013680, len 512
Versions: Boot 1, Update 0
Trying Boot partition at 0x20000
Loading header 512 bytes from 0x20000 to 0x8DFFFE00
SC SPI: Read 0x20000 -> 0x8DFFFE00, len 512
Loading image 128664 bytes from 0x20200 to 0x8E000000...
SC SPI: Read 0x20200 -> 0x8E000000, len 128664
done
Boot partition: 0x8DFFFE00 (sz 128664, ver 0x1, type 0x601)
Checking integrity...done
Verifying signature...done
Successfully selected image in part: 0
Firmware Valid
SC SPI: Read 0x1FFFFFC -> 0x80013880, len 4
Loading elf at 0x8E000000
Found valid elf64 (little endian)
Program Headers 1 (size 56)
Load 21304 bytes (offset 0x1000) to 0x8E000000 (p 0x8E000000)
Clear 16392 bytes at 0x8E000000 (p 0x8E000000)
Entry point 0x8E0012B8
Booting at 0x8E0012B8
FDT: Invalid header! -1
QSPI: Using System Controller SPI services
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PolarFire SoC MPFS250 wolfBoot demo Application
Copyright 2025 wolfSSL Inc
GPL v3
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