ARM: configs: clean up multi_v5_defconfig

ARM: configs: clean up multi_v5_defconfig

Clean up some cruft accumulated over time:
- The default definition of CONFIG_ZBOOT_ROM_* got fixed in commit
  39c3e304567a ("ARM: 8984/1: Kconfig: set default ZBOOT_ROM_TEXT/BSS
  value to 0x0"), so we don't need the explicit setting anymore.
- CONFIG_ABX500_CORE now explicitly depends on the ARMv7 ARCH_U8500,
  so we don't need to disable that symbol explicitly anymore.
- CONFIG_DEBUG_FS was just moved around in the generated defconfig.

No change to the generated .config or savedefconfig.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20220317183043.948432-5-andre.przywara@arm.com'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>