common: dma-mapping: introduce mmap method

Introduce new generic mmap method with attributes argument.

This method lets drivers to create a userspace mapping for a DMA buffer
in generic, architecture independent way.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>