configs: toradex-smarc-imx95: set spl_stack

configs: toradex-smarc-imx95: set spl_stack

The SPL_STACK config option now depends on having SPL_HAVE_INIT_STACK
defined. This made savedefconfig dropping SPL_STACK when sending the
initial configuration.
Note that SPL/U-Boot are able to boot linux from mass storage with
SPL_STACK not set but other use cases might run out of stack or
overlap with other RAM use.

Compare with:
commit d6a53f523afe ("spl: Add an SPL_HAVE_INIT_STACK option")
commit 25fefa05d732 ("configs: Resync with savedefconfig")

Fixes: ff0540fcfe49 ("board: toradex: add Toradex SMARC iMX95")
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Francesco Dolcini <francesco.dolcini@toradex.com>