amba-clcd: separate ioremap framebuffer from DMA implementation

amba-clcd: separate ioremap framebuffer from DMA implementation

The amba-clcd device can be configured to use either DMA or, when this
feature is not available, an ioremapped frambuffer in static ram.

In the case of the latter, we must take care not to pass ioremapped
addresses to dma_common_mmap, since this expects only addresses from
dma_mmap_coherent, which reside in the kernel linear mapping.

This patch reworks the fb initialisation code so that either DMA or IO
implementations of the mmap/remove functions are chosen as appropriate.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>