Revert "target: add target->type->has_mmu fn"
This patch introduced a bug preventing flash writes from working on Cortex-M3 targets like the STM32. Moreover, it's the wrong approach for handling no-MMU targets. The right way to handle no-MMU targets is to provide accessors for physical addresses, and use them everywhere; and any code which tries to work with virtual-to-physical mappings should use a identity mapping (which can be defaulted). And ... we can tell if a target has an MMU by seeing if it's got an mmu() method. No such methood means no MMU. Signed-off-by: David Brownell <email@example.com>