ARM: 8633/1: nommu: allow mmap when !CONFIG_MMU

commit ab6494f0 ("nommu: Add noMMU support to the DMA API") have
add CONFIG_MMU compilation flag but that prohibit to use dma_mmap_wc()
when the platform doesn't have MMU.

This patch call vm_iomap_memory() in noMMU case to test if addresses
are correct and set vma->vm_flags rather than all return an error.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>