soc: xlnx: zynqmp: fix vectors and SRAM MPU region priority order

Place the 'vectors' region configuration behind the 'sram' and
'rom_region' configurations so that the MPU region for the
vectors takes precedence over the 'sram' region due to higher
region index = higher priority when resolving memory properties
/ permissions for overlapping regions. This is required for the
vectors to work properly if the SRAM base address is also at 0x0.

Fixes #96688.

Signed-off-by: Immo Birnbaum <mail@birnbaum.immo>