Fix XSPI FIFO indexing, PIC32 PFSWAP toggle, and small-stack key zeroize

[aidangarske]

F-6588, F-6560, F-6567

[Copilot]

Pull request overview

This PR fixes three low-level correctness issues in wolfBoot’s hardware/crypto paths and adds unit tests to prevent regressions: LS1028A XSPI TX FIFO register indexing, PIC32C dual-bank PFSWAP toggling (bit preservation on RMW), and encryption key cache zeroization on the small-stack path.

Changes:

• Fix LS1028A XSPI TX FIFO fill to use word indexing (j/4) instead of byte-stride pointer arithmetic.
• Fix PIC32C FCW_SWAP PFSWAP update to clear/set only the PFSWAP bit while preserving other register bits.
• Ensure hal_set_key() zeroizes ENCRYPT_CACHE even when WOLFBOOT_SMALL_STACK is enabled, and add unit tests covering all three fixes.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tools/unit-tests/unit-xspi-tfd-index.c	Adds a unit test that reproduces the XSPI TX FIFO mis-indexing and verifies the corrected word-index behavior.
tools/unit-tests/unit-pic32-pfswap.c	Adds a unit test validating correct PFSWAP toggling and preservation of unrelated FCW_SWAP bits.
tools/unit-tests/unit-enc-key-zeroize.c	Adds a unit test ensuring hal_set_key() zeroizes the (static) encryption cache on the small-stack configuration.
tools/unit-tests/Makefile	Registers and builds the new unit tests, including required per-test flags and sources for the encryption test.
src/libwolfboot.c	Updates hal_set_key() to zeroize ENCRYPT_CACHE regardless of WOLFBOOT_SMALL_STACK (still respecting existing guards).
hal/pic32c.c	Fixes FCW_SWAP RMW masking to clear the PFSWAP bit correctly (&= ~FCW_SWAP_PFSWAP).
hal/nxp_ls1028a.c	Fixes XSPI TFD pointer arithmetic to use word indexing for FIFO writes in both full and remainder loops.

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