ARM: 8646/1: mmu: decouple VECTORS_BASE from Kconfig

For MMU configurations, VECTORS_BASE is always 0xffff0000, a macro
definition will suffice.

For no-MMU, exception base address is dynamically determined in
subsequent patches. To preserve bisectability, now make the
macro applicable for no-MMU scenario too.

Thanks to 0-DAY kernel test infrastructure that found the
bisectability issue. This macro will be restricted to MMU case upon
dynamically determining exception base address for no-MMU.

Once exception address is handled dynamically for no-MMU,
VECTORS_BASE can be removed from Kconfig.

Signed-off-by: afzal mohammed <afzal.mohd.ma@gmail.com>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>