relocate uImage payload to ih_load under RAMBOOT

[dgarske]

Under WOLFBOOT_USE_RAMBOOT, a WOLFBOOT_UBOOT_LEGACY (uImage) payload with a non-zero ih_load that differs from the RAMBOOT staging address boots corrupt: wolfBoot_start() rewrites the jump target (load_address = ih_load) but never copies the payload there, because the generic copy-to-RAM memcpy is compiled out under RAMBOOT -- so do_boot() jumps to memory that was never written. This is reachable on the shipped zynqmp/zynq7000/versal configs (all set EXT_FLASH+NO_XIP and enable WOLFBOOT_UBOOT_LEGACY), just not on today's raw-zImage test path; any mkimage-wrapped kernel with a real ih_load hits it. The fix relocates the staged payload from os_image.fw_base to ih_load via overlap-safe memmove when the two differ, mirroring the non-RAMBOOT path (the ih_load == 0 Linux/PPC path is untouched). Added a host regression test (tools/unit-tests/unit-update-ram-uboot.c) that drives the real wolfBoot_start() flow with -DWOLFBOOT_UBOOT_LEGACY and asserts the payload lands at ih_load across four cases (coincident / higher / lower-overlap / ih_load==0); verified it fails the relocation cases when the fix is reverted. No Zynq/Versal hardware locally -- validated via the host check harness.

Fixes #827

[Copilot]

Pull request overview

This PR fixes a RAMBOOT-specific boot corruption when booting U-Boot legacy (uImage) payloads whose non-zero ih_load differs from the RAMBOOT staging location. Under WOLFBOOT_USE_RAMBOOT, wolfBoot_start() updates the jump target to ih_load but (prior to this change) did not relocate the already-staged payload there because the generic copy-to-RAM path is compiled out.

Changes:

• Relocate the staged uImage payload to ih_load via overlap-safe memmove() under WOLFBOOT_USE_RAMBOOT when ih_load != 0 and differs from os_image.fw_base.
• Add a host regression test that drives the real wolfBoot_start() flow under WOLFBOOT_USE_RAMBOOT + WOLFBOOT_UBOOT_LEGACY, covering coincident, higher, lower-overlap, and ih_load == 0 cases.
• Wire the new unit test into the unit-test build/run Makefile.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/update_ram.c	Adds RAMBOOT-only payload relocation to ih_load for uImage legacy boot to prevent jumping to unwritten memory.
tools/unit-tests/unit-update-ram-uboot.c	New regression test exercising uImage ih_load relocation behavior under RAMBOOT across multiple address/overlap cases.
tools/unit-tests/Makefile	Adds unit-update-ram-uboot to the test list and build rules with required defines and link objects.

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