arm: mach-k3: Let the compiler size the mem_map lists

NR_MMU_REGIONS is a copy/paste from another platform that extends
this list later. We do not do that, so let the list be the size
of the initializer list.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>