Add NXP S32K1xx Support

This PR adds full wolfBoot support for the NXP S32K1xx automotive microcontroller family (S32K142, S32K144, S32K146, S32K148).

Summary

Adds a complete bare-metal HAL implementation for the S32K1xx Cortex-M4F family with sector-swap firmware update capability. Tested on S32K142EVB with successful firmware updates.

Features

HAL Implementation (hal/s32k1xx.c, hal/s32k1xx.h):

• Flash programming using FTFC controller (phrase-level 8-byte writes)
• LPUART1 debug output at 115200 baud
• Clock configuration using FIRC (48 MHz internal RC oscillator)
• Watchdog management (disable during boot, optional enable for production)
• Flash Configuration Field (FCF) for security settings

Test Application (test-app/app_s32k1xx.c):

• Interactive console with commands: status, trigger, success, reboot, help
• LED indicators: Green LED for v1, Blue LED for v2+
• XMODEM firmware update support
• Partition and keystore information display

Configuration Files:

• config/examples/nxp-s32k142.config - 256KB Flash, 32KB SRAM, 2KB sectors
• config/examples/nxp-s32k144.config - 512KB Flash, 64KB SRAM, 4KB sectors
• config/examples/nxp-s32k146.config - 1MB Flash, 128KB SRAM, 4KB sectors
• config/examples/nxp-s32k148.config - 2MB Flash, 256KB SRAM, 4KB sectors

Tooling:

• tools/scripts/nxp-s32k142-flash.sh - Automated build, sign, and flash script using J-Link

Memory Layout (S32K142)

Important Configuration Requirements

• NVM_FLASH_WRITEONCE=1 - Required because S32K1xx flash cannot be reprogrammed without erase
• RAM_CODE=1 - Required because flash cannot be read while being programmed

Build & Test

# Build wolfBoot
cp config/examples/nxp-s32k142.config .config
make clean && make

# Build test app
make test-app/image.bin

# Sign images
./tools/keytools/sign --ecc256 --sha256 test-app/image.bin wolfboot_signing_private_key.der 1
./tools/keytools/sign --ecc256 --sha256 test-app/image.bin wolfboot_signing_private_key.der 2

Files Changed

• New files: hal/s32k1xx.c, hal/s32k1xx.h, hal/s32k1xx.ld, test-app/app_s32k1xx.c, test-app/ARM-s32k1xx.ld
• Config files: 4 new example configurations for S32K142/144/146/148
• CI: Added build tests for all S32K1xx variants
• Documentation: Added comprehensive S32K1xx section to docs/Targets.md

Testing

Verified on S32K142EVB:

• wolfBoot boots successfully and validates firmware signature
• Firmware update via sector swap completes successfully
• Test application marks update as successful
• Version rollback works correctly