boards: st: stm32h573i_dk: Add board variant for app in external flash

Restore old internal flash layout as default and make app in external
flash a new board variant

Switch mcuboot to use swap mode and remove the no longer required
scratch partitions from the internal and external flash layout.

Introduce a 'soc-nv-flash' node in the stm32h573i_dk board DTS file
to define the external flash memory parameters used for MCUBoot
integration. This way BOOT_MAX_IMG_SECTORS_AUTO can be used to
automatically calculate the maximum number of image sectors based
on the actual external flash configuration.

Signed-off-by: Tim Pambor <tim.pambor@codewrights.de>
8 files changed