ARM: fix building NOMMU ARMv4/v5 kernels

The removal of the old-style irq entry broke obscure NOMMU
configurations on machines that have an MMU:

ld.lld: error: undefined symbol: generic_handle_arch_irq
 referenced by kernel/entry-armv.o:(__irq_svc) in archive arch/arm/built-in.a

A follow-up patch to convert nvic to the generic_handle_arch_irq()
could have fixed this by removing the Kconfig conditional, but did
it differently.

Change the Kconfig logic so ARM machines now unconditionally
enable the feature.

I have also submitted a patch to remove support for the configurations
that broke, but fixing the regression first is a trivial and correct
change.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 54f481a2 ("ARM: remove old-style irq entry")
Fixes: 52d24087

 ("irqchip: nvic: Use GENERIC_IRQ_MULTI_HANDLER")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>