arm: Remove rel.dyn from SPL linker scripts

arm: Remove rel.dyn from SPL linker scripts

As of v2026.01, no platforms contain any rel.dyn sections in their xPL
phase images. Their inclusion in linker scripts initially was an
oversight as part of taking the full U-Boot linker scripts and modifying
them down. Then in commit 8b0ebe054bb3 ("arm: Update linker scripts to
ensure appended device tree is aligned") these sections were used to
force correct alignment for the device tree. This however, lead to a
different problem.

That problem is that when we do not have a separate BSS section in SPL
we instead would overlay the BSS with the rel.dyn section, in the common
linker script case. This in turn lead to creating an incorrectly sized
BSS "pad" file sometimes (depending on arbitrary changes within the rest
of the binary itself). This in turn lead to the dtb being in the wrong
location in the binary and not found at run time.

This commit fixes a few things:
- Remove the rel.dyn section from all ARM SPL linker scripts.
- In turn, this moves the dtb alignment statement in to another section.
- For ast2600 which uses CONFIG_POSITION_INDEPENDENT we need to keep the
  symbols however.

Tested-by: Fabio Estevam <festevam@gmail.com>
Reported-by: Fabio Estevam <festevam@gmail.com>
Co-developed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Chia-Wei, Wang <chiawei_wang@aspeedtech.com>
Signed-off-by: Tom Rini <trini@konsulko.com>