- If we have no memory registered in mmu_init() it's a critical bug.
  panic in this case.
- If we do not have a ttb when dma_alloc_coherent or remap_range is
  called it's also a critical bug. Panic in this case.
- if find_pte is called with an address outside our memory banks dump
  the memory banks and the address to give more clue what went wrong.

Also add some hints what might went wrong to the code.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>